presentation on heart chambers

Cardiovascular System

• It is know as the “transportation” system of the body

Structures Include:

-Blood Vessels

Layers of the Heart

• Endocardium
• Smooth layer
• Lines the interior
• Valves are made from this layer
• Muscle layer
• Thickest layer
• Thin, outermost layer
• Joins with serous lining outside the heart to form the Pe ricardium
• Separates the left and right heart
• Interatrial – top part of the septum
• Interventricular – bottom part of the septum

The Four Chambers

• Right Atrium
• Right Ventricle
• Left Atrium
• Left Ventricle
• Right Atrium – receives blood from the superior and inferior vena cava
• Right Ventricle – pumps blood to the lungs
• Left Atrium – receives oxygenated blood from the lungs
• Left Ventricle – pumps oxygenated blood to the rest of the body, strongest chamber
• Valves are important to control the flow of blood from one chamber of the heart to another .
• Valves allow blood to flow in only one direction

Heart Valves

Tricuspid valve – opening between right atria and right ventricle

Pulmonary semilunar valve – opening between right ventricle and pulmonary artery

Mitral valve (also called bicuspid) – opening between left atrium and left ventricle

Aortic semilunar valve – located between left ventricle and aorta

• Chordae tendineae – threads, keep valve flaps from flipping up into the atria
• Right Atrioventricular (tricuspid valve) – between the right atrium and right ventricle, has 3 flaps, prevents blood from flowing back into the right atrium
• Pulmonic (semilunar valve) – between the right ventricle and the pulmonary artery, prevents blood from flowing back into the right ventricle
• Left Atrioventricular (bicuspid valve) – between the left atrium and left ventricle, prevents blood from flowing back into the left atrium, has 2 flaps (mitral valve)
• Aortic Valve – between the left ventricle and the aorta, prevents blood from flowing back into the left ventricle

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The Heart's Chambers and Valves

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The function of the heart is to pump the blood that bathes and nourishes every organ of the body. The blood carries the oxygen and nutrients vital to the tissues, and it also carries waste products away from the tissues. If the pumping action of the heart is disrupted for any reason, the body’s organs begin to fail very quickly. So life itself is dependent on the efficient, continuous operation of the heart.  

The heart is a muscular organ roughly the size of your fist. As the heart muscle contracts, it propels the blood out into the vascular system. The heart’s chambers and valves are arranged to direct the flow of the blood as the heart beats.

Heart’s Chambers and Valves

The heart has two “sides.” The right side of the heart accepts “used” blood that is returning from the tissues of the body, and pumps that blood into the lungs, where it is replenished with oxygen. The left side of the heart accepts replenished blood from the lungs, and then pumps that blood out to all the body’s organs.

Each side of the heart has two chambers, for a total of four chambers. The two ventricles (right and left) are muscular chambers capable of propelling the blood out of the heart. The right ventricle pumps blood to the lungs, and the left ventricle pumps blood to all other organs.

The two atria (right and left) accept the blood returning to the heart (from the body’s tissues and from the lungs, respectively). At just the right moment, the right and left atria empty their accumulated blood into the right and left ventricles. 

The  four heart valves  (tricuspid, pulmonary, mitral and aortic) open and close at just the right moment to keep the blood moving in the proper direction through the heart.

It is helpful to visualize the heart functioning as two separate pumps, working in series; the right heart pump, and the left heart pump. 

The Right Heart Pump

The right heart pump consists of the right atrium, tricuspid valve, right ventricle, pulmonic valve, and pulmonary artery. Its job is to make sure “used” blood gets reloaded with oxygen. Oxygen-poor blood returning to the heart from the body’s tissues enters the right atrium. When the atria contract, the tricuspid valve opens and allows the blood to be pumped from the right atrium to the right ventricle. Then, when the right ventricle contracts, the tricuspid valve closes (to prevent blood from washing backwards into the right atrium), and the pulmonic valve opens — so blood is ejected from the right ventricle and out to the pulmonary artery and the lungs, where it is replenished with oxygen.

• Read about tricuspid regurgitation.
• Read about pulmonary artery hypertension.

The Left Heart Pump

The left heart pump consists of the left atrium, mitral valve, left ventricle, aortic valve, and aorta. Its job is to pump oxygen-rich blood out to the body’s tissues. Blood returning to the heart from the lungs enters the left atrium. When the atria contract, the mitral valve opens and allows the blood to enter the left ventricle. When the left ventricle contracts a moment later, the mitral valve closes and the aortic valve opens. Blood is propelled out of the left ventricle, across the aortic valve, and out to the body.

• Read about mitral stenosis.
• Read about mitral regurgitation.
• Read about aortic stenosis.
• Read about aortic regurgitation.

The Cardiac Cycle

You may hear about a concept called the cardiac cycle. Simply, the “cardiac cycle” is a way doctors have of dividing the work of the heart into two phases — the diastolic phase and the systolic phase. 

During the diastolic phase of the cardiac cycle, the atria are contracting to fill the two ventricles with blood, and the ventricles are “relaxing” in between heart beats. The tricuspid and mitral valves are open during the diastolic phase to allow blood to flow into the ventricles, and the pulmonic and aortic valves are closed to prevent blood from washing backwards into the ventricles. 

During the systolic phase, the two ventricles are contracting to propel blood out to the lungs (right ventricle) and out to the rest of the body (left ventricle). The right atrium is filling with “used” blood from the tissues, and the left atrium is filling with oxygenated blood from the lungs. The tricuspid and mitral valves are closed during systole, and the pulmonic and aortic valves are open.

The concept of the cardiac cycle is useful in several ways. For instance, when we measure blood pressure, we are measuring the pressure in the arteries during both phases of the cardiac cycle — systolic and diastolic. So, blood pressure is reported as two numbers, such as 120/80. Here, the systolic blood pressure (the arterial pressure at the moment the ventricles are beating) is 120 mmHg, and the diastolic pressure (the pressure during ventricular relaxation) is 80 mmHg.

• Read about measuring blood pressure.

Also, when cardiologists talk about heart failure, they often specify whether the cardiac dysfunction primarily affects the systolic portion of cardiac function (as in  dilated cardiomyopathy ), or the diastolic portion (as in  diastolic dysfunction ). Proper treatment requires making this distinction. 

Read about the anatomy of the normal coronary arteries.

Finally, it is important to note that the sequence and timing involved in the cardiac cycle — the opening and closing of the four valves and the pumping and relaxing of the four chambers — is critical to normal cardiac function. This timing and sequencing is critically dependent on the  cardiac electrical system, which you can read about here .

NIH National Heart, Lung, and Blood Institute. How the heart works .

Lang RM, Badano LP, Mor-Avi V, et al. Recommendations for Cardiac Chamber Quantification by Echocardiography in Adults: An Update From the American Society of Echocardiography and the European Association of Cardiovascular Imaging. J Am Soc Echocardiogr 2015; 28:1.

• Otto CM. Textbook of Clinical Echocardiography, 4th edition, Saunders Elsevier, 2009.

By Richard N. Fogoros, MD Richard N. Fogoros, MD, is a retired professor of medicine and board-certified in internal medicine, clinical cardiology, and clinical electrophysiology.

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At the Heart of It All: Anatomy and Function of the Heart

© 2024 Visible Body

The heart is a hollow, muscular organ that pumps oxygenated blood throughout the body and deoxygenated blood to the lungs. This key circulatory system structure is comprised of four chambers. One chamber on the right receives blood with waste (from the body) and another chamber pumps it out toward the lungs where the waste is exhaled. One chamber on the left receives oxygen-rich blood from the lungs and another pumps that nutrient-rich blood into the body. Two valves control blood flow within the heart’s chambers, and two valves control blood flow out of the heart.

1. The Heart Wall Is Composed of Three Layers

The muscular wall of the heart has three layers. The outermost layer is the epicardium (or visceral pericardium). The epicardium covers the heart, wraps around the roots of the great blood vessels, and adheres the heart wall to a protective sac. The middle layer is the myocardium . This strong muscle tissue powers the heart’s pumping action. The innermost layer, the endocardium , lines the interior structures of the heart.

2. The Atria Are the Heart’s Entryways for Blood

The left atrium and right atrium are the two upper chambers of the heart. The left atrium receives oxygenated blood from the lungs. The right atrium receives deoxygenated blood returning from other parts of the body. Valves connect the atria to the ventricles, the lower chambers. Each atrium empties into the corresponding ventricle below.

3. Each Heart Beat Is a Squeeze of Two Chambers Called Ventricles

The ventricles are the two lower chambers of the heart. Blood empties into each ventricle from the atrium above, and then shoots out to where it needs to go. The right ventricle receives deoxygenated blood from the right atrium, then pumps the blood along to the lungs to get oxygen. The left ventricle receives oxygenated blood from the left atrium, then sends it on to the aorta. The aorta branches into the systemic arterial network that supplies all of the body.

4. The Valves Are Like Doors to the Chambers of the Heart

Four valves regulate and support the flow of blood through and out of the heart. The blood can only flow one way—like a car that must always be kept in drive. Each valve is formed by a group of folds, or cusps, that open and close as the heart contracts and dilates. There are two atrioventricular (AV) valves, located between the atrium and the ventricle on either side of the heart: The tricuspid valve on the right has three cusps, the mitral valve on the left has two. The other two valves regulate blood flow out of the heart. The aortic valve manages blood flow from the left ventricle into the aorta. The pulmonary valve manages blood flow out of the right ventricle through the pulmonary trunk into the pulmonary arteries.

5. The Cardiac Cycle Includes All Blood Flow Events the Heart Accomplishes in One Complete Heartbeat

The muscular wall of the heart powers contraction and dilation. Each contraction and relaxation is a heartbeat. Ventricular contractions, called systole , force blood out of the heart through the pulmonary and aortic valves. Diastole occurs when blood flows from the atria to fill the ventricles.

Download Heart Lab Manual

External Sources

“ How the Heart Works, ” an overview of heart function from the University of Michigan Health.

A description of the heart from the 1918 edition of Gray's Anatomy of the Human Body.

Visible Body Web Suite offers thousands of models to help understand and communicate how the human body looks and works.

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Functions of the Blood

Blood Vessels: The Circulatory Network

Pulmonary and Systemic Circulation

Circulatory System Pathologies

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• < Back To How the Heart Works
• What the Heart Looks Like
• How Blood Flows through the Heart
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MORE INFORMATION

How the Heart Works What the Heart Looks Like

Language switcher.

Your heart is in the center of your chest, near your lungs. It has four hollow chambers surrounded by muscle and other heart tissue. The chambers are separated by heart valves, which make sure that the blood keeps flowing in the right direction. Read more about heart valves and how they help blood flow through the heart .

Heart chambers

The two upper chambers of your heart are called atria , and the two lower chambers are called  ventricles . Blood flows from the body and lungs to the atria and from the atria to the ventricles. The ventricles pump blood out of the heart to the lungs and other parts of the body. An internal wall of tissue divides the right and left sides of your heart. This wall is called the septum.

The four chambers of the heart.  Medical Animation Copyright © 2022 Nucleus Medical Media, All rights reserved .

Heart tissue

The heart is made of three layers of tissue.

• Endocardium is the thin inner lining of the heart chambers and also forms the surface of the valves.
• Myocardium is the thick middle layer of muscle that allows your heart chambers to contract and relax to pump blood to your body.
• Pericardium is the sac that surrounds your heart. Made of thin layers of tissue, it holds the heart in place and protects it. A small amount of fluid between the layers helps reduce friction between the beating heart and surrounding tissues.

Learn about the heart muscle, which is arranged in a unique pattern to help your blood pump more efficiently. Medical Animation Copyright © 2022 Nucleus Medical Media, All rights reserved .

Some conditions can affect the heart's tissue.

• Cardiomyopathy   is when the heart muscle becomes enlarged, thick, or rigid. As cardiomyopathy worsens, the heart becomes weaker and is less able to pump blood through the body and maintain a normal electrical rhythm.
• Heart inflammation is inflammation  in one or more of the layers of tissue in the heart, including the pericardium, myocardium, or endocardium. This can lead to serious complications, including  heart failure ,  cardiogenic shock , or irregular heart rhythm.
• Congenital heart disease is when the heart does not develop in the typical way. A congenital heart defect can happen at any point during development of an unborn baby, or embryo, inside the pregnant mother.  

Learn more about how the NHLBI supports heart health and heart disease research through the Framingham Heart Study , the Strong Heart Study , and the Jackson Heart Study .

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StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

StatPearls [Internet].

Anatomy, thorax, heart.

Ibraheem Rehman ; Afzal Rehman .

Affiliations

Last Update: August 28, 2023 .

• Introduction

The heart is a muscular organ situated in the center of the chest behind the sternum. It consists of four chambers: the two upper chambers are called the right and left atria, and the two lower chambers are called the right and left ventricles. The right atrium and ventricle together are often called the right heart, and the left atrium and left ventricle together functionally form the left heart. [1] [2] [3] [4]

• Structure and Function

The heart consists of four chambers organized into two pumps (right and left) to provide blood flow to the systemic and pulmonary circulations. The right atrium receives deoxygenated blood from the entire body except for the lungs (the systemic circulation) via the superior and inferior vena cavae. Also, deoxygenated blood from the heart muscle itself drains into the right atrium via the coronary sinus. The right atrium, therefore, acts as a reservoir to collect deoxygenated blood. From here, blood flows through the tricuspid valve to fill the right ventricle, which is the main pumping chamber of the right heart.

The right ventricle pumps blood through the right ventricular outflow tract, across the pulmonic valve, and into the pulmonary artery that distributes it to the lungs for oxygenation. In the lungs, the blood oxygenates as it passes through the capillaries, where it is close enough to the oxygen in the alveoli of the lungs. This oxygenated blood is collected by the four pulmonary veins, two from each lung. All four of these veins open into the left atrium that acts as a collection chamber for oxygenated blood. As with the right atrium, the left atrium passes the blood onto its ventricle both by passive flow and active pumping. Oxygenated blood thus fills the left ventricle, passing through the mitral valve. The left ventricle is the main pumping chamber of the left heart, then pumps, sending freshly oxygenated blood to the systemic circulation through the aortic valve. The cycle is then repeated all over again in the next heartbeat. 

All four valves of the heart mentioned above have a singular purpose: allowing forward flow of blood but preventing backward flow.

Conduction System

An electrical conduction system regulates the pumping of the heart and the timing of contraction of various chambers.  Heart muscle contracts in response to the electrical stimulus received. The sinus node, which is the main pacemaker of the heart, is situated at the junction of the superior vena cava and the right atrium. It rhythmically generates an electrical discharge about 70 times a minute. This electrical signal is carried to the left atrium via the Bachmann’s bundle. Conduction occurs through the right atrial muscle to the atrioventricular node (AV node), located in the triangle of Koch, a small triangular area formed by the tricuspid valve, tendon of Todaro, and lip of the coronary sinus ostium. The AV node receives the electrical signal and conducts it to the bundle of His with some delay. This delay allows the emptying of the atria into the ventricles before the ventricles contract in response to the electrical signal.

The bundle of His divides into the right and left bundles that successively branch into thousands of small branches called Purkinje fibers. The His-Purkinje tree serves to rapidly conduct the electrical signal to all parts of both ventricles to produce a near-simultaneous contraction of all parts of both ventricles, producing a uniform and coordinated squeeze. [5] [6] [7] [8]

The heart develops from two endocardial tubes that merge, loop, and septate to form the heart. During the intrauterine stage, the septum between the two atrial is open, and a ductus connects the pulmonary artery to the aorta, effectively bypassing the pulmonary circulation because the lungs are not functional. Rapidly after birth, these two connections close, establishing separate pulmonary and system circulations. [9]

• Blood Supply and Lymphatics

The heart is supplied by two coronary arteries: the left main coronary artery and the right coronary artery. The left main coronary artery carries 80% of the flow to the heart muscle. It is a short artery that divides into two branches, (1) the left anterior descending artery that supplies anterior two-thirds of the inter-ventricular septum and adjoining part of the left ventricular anterior wall, and (2) the circumflex coronary artery that supplies blood to the lateral and posterior portions of the left ventricle.

The right coronary artery and its branches supply the right ventricle, right atrium, and left ventricle's inferior wall.

Coronary arteries and veins course over the surface of the heart. Most coronary veins coalesce into the coronary sinus that runs in the left posterior atrioventricular groove and opens into the right atrium. Other small veins, called thebesian veins, open directly into all four chambers of the heart.

Small lymphatic vessels form a dense network beneath the epicardium and endocardium of the ventricles and open into a lymphatic duct in the atrioventricular groove. However, the detailed lymphatic anatomy of the human heart has not been worked out.

The sinus node and the AV node are both supplied by sympathetic nerve fibers from the sympathetic ganglia and parasympathetic fibers through the vagus nerve and parasympathetic ganglia behind the heart.

The heart is a muscular organ. It has no bones. Sheets of muscle fibers are arranged over a fibrous skeleton to give the heart chambers their shapes. However, the atrial muscle is completely separated from the ventricular muscle by a fibrous atrioventricular scaffolding such that no electrical conduction can occur between the two, except through the AV node. 

• Physiologic Variants

The general structure of the heart is quite uniform in healthy individuals. However, some variations do occur. The heart is arranged more horizontally in the chest in short and obese individuals, while it is more vertical in tall and thin people. An athlete’s heart may be physically larger. Coronary arteries show variations in branching patterns and relative sizes.

• Surgical Considerations

Cardiac valves can become fibrosed and calcific with age or disease, producing clinically significant stenosis requiring surgical or trans-catheter replacement. Similarly, valves may become incompetent, allowing backward flow called regurgitation, also necessitating replacement or repair. [10]

Coronary arteries can become clogged with thrombus or atherosclerotic plaque, causing reduced blood supplies to cardiac muscle. This may result in angina or myocardial infarction and often requires revascularization.

• Clinical Significance

The heart is a vital organ. If the heart stops, cessation of blood flow and oxygen supply will occur, leading to irreversible brain damage within 4 to 5 minutes. Cessation or impairment of cardiac function may occur due to a lack of blood supply to the cardiac muscle (coronary artery disease), stenosis or regurgitation in cardiac valves (valvular heart disease), intrinsic weakness of heart muscle (cardiomyopathy), or ineffective cardiac rhythms.

• Other Issues

In six per 1000 live births, congenital cardiac malformations occur. Ventricular septal defects (VSD), atrial septal defects, and tetralogy of Fallot among the commonest.  Tetralogy of Fallot consists of a combination of VSD of the membranous portion of the interventricular septum, stenosis of the orifice of the pulmonary artery, the aortic orifice overriding the VSD, and hypertrophy of the right ventricle. This requires surgical correction, usually at an early age.

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Anatomy of the Heart Henry Vandyke Carter, Public Domain, via Wikimedia Commons

The diagram shows a healthy heart during pumping and filling. Also a heart suffering from Tetralogy of Fallot which are four different malformations and are usually known as Blue Baby Syndrome. Contributed by Wikimedia Commons, Mariana Ruiz (Public Domain) (more...)

Disclosure: Ibraheem Rehman declares no relevant financial relationships with ineligible companies.

Disclosure: Afzal Rehman declares no relevant financial relationships with ineligible companies.

This book is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits others to distribute the work, provided that the article is not altered or used commercially. You are not required to obtain permission to distribute this article, provided that you credit the author and journal.

• Cite this Page Rehman I, Rehman A. Anatomy, Thorax, Heart. [Updated 2023 Aug 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

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Anatomy of the Heart

Jul 25, 2014

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Anatomy of the Heart. The heart is located in the chest cavity, surrounded by the pericardial sac, in the anterior portion of the mediastinum. . The Pericardium. Pericardial cavity. The pericardium is a double-walled sac (pericardial sac) that encloses the heart. Parietal pericardium.

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Presentation Transcript

The heart is located in the chest cavity, surrounded by the pericardial sac, in the anterior portion of the mediastinum.

The Pericardium Pericardial cavity The pericardium is a double-walled sac (pericardial sac) that encloses the heart. Parietal pericardium Visceral pericardium (epicardium) Mesothelium Pericarditis is a disorder caused by inflammation of the pericardium, the sac-like covering of the heart. Areolar tissue Fibrous tissue Pericarditis can be caused by bacterial, fungal, or viral infections. It may also be a result of injury or trauma to the chest, esophagus, or heart. Pain occurs as a result of the inflamed pericardium rubbing against the heart.

The Heart Wall Parietal pericardium Areolar tissue Areolar tissue Pericardial cavity MYOCARDIUM (cardiac muscle tissue) ENDOCARDIUM EPICARDIUM Endothelium Mesothelium Visceral pericardium Mesothelium Areolar tissue Fibrous tissue Endocarditis is inflammation of the inside lining of the heart chambers and heart valves (endocardium). Most people who develop endocarditis have heart disease of the valves.

An Introduction to the Cardiovascular System GasExchange Systemic Pulmonary Circuit Circuit Capillary Lung Venule Arteriole Pulmonary arteries Pulmonary veins O2 poor, CO2 rich blood O2 rich, CO2 poor blood Wastes Nutrients O2 CO2 CO2 O2 Venae cavae Aorta Capillary Tissue Venule Arteriole

Cardiovascular System: Pulmonary Circuit It carries blood to the lungs for gas exchange and returns it to the heart. Systemic Circuit It supplies blood to every organ of the body, including the lungs and the heart itself. Blood Vessels: Arteries They carry blood away from the heart. Veins They carry blood back to (toward) the heart. Capillaries They connect the arteries with the veins.

Gas exchange Pulmonary Circuit It carries blood to the lungs for gas exchange and returns it to the heart. O2rich blood through VEINS O2poor blood through ARTERIES Systemic Circuit It supplies blood to every organ of the body, including the heart itself. O2rich blood through ARTERIES O2poor blood through VEINS

Internal Anatomy and Organization Gas exchange Poor oxygen blood Pulmonary Arteries (2) Reach oxygen blood Superior vena cava Coronary sinus Inferior vena cava Pulmonary veins (4) Pulmonary Trunk RIGHT ATRIUM LEFT ATRIUM To the rest of the body RIGHT VENTRICLE LEFT VENTRICLE Aorta

Superior vena cava It drains oxygen-poor blood from tissues and organs superior to the diaphragm to the right atrium. Aorta Pulmonary trunk It carries oxygen-rich blood from the left ventricle to the whole body. It carries oxygen-poor blood from the right ventricle to the lungs. Pulmonary veins (4) Inferior vena cava They carry oxygen-rich blood from the lungs to the left atrium. It drains oxygen-poor blood from tissues and organs inferior to the diaphragm to the right atrium. Coronary sinus (no shown) It drains oxygen-poor blood from the heart tissues to the right atrium.

The Heart Valves The heart has two pairs of one-way valves that prevent the backflow when the chambers contract It prevents back flow of blood from the pulmonary trunk to the RV Aortic semilunar valve It prevents back flow of blood from the LV to the LA It prevents back flow of blood from the RV to the RA Left AV (bicuspid) valve Pulmonary semilunar valve It prevents back flow of blood from the aorta to the LV Right AV (tricuspid) valve

Heart Sounds During ventricular systole (contraction) the two AV close at the same time and produce the first sound referred asLubb. Lubb Dupp Dupp Lubb When the ventricles relax (diastole) the two semilunar valves close at the same time and produce the second sound referred asDubb.

Heart Sounds The heart sounds are described as a lubb-dupp sound First Sound ( “lubb” ): It is the strongest one. It is produced by the closing of the AV valves Second Sound ( “dupp” ):It is produced by the closing of the semilunar valves Normal valves produce high pitch sound Incompetent valves (that do not close completely) produce a switching sound as blood flows back creating abnormal sounds Heart Murmur: It is a sound produced by regurgitation through valves

Ligamentum arteriosum Four openings of the pulmonary veins Remnant of ductus arteriosum Opening of superior vena cava Aortic arch (Remnant of foramen oval) Pulmonary trunk Fossaovalis Pulmonary veins Opening of coronary sinus Aortic semilunar valve Opening of inferior vena cava It prevents back flow of blood from the aorta to the LV Left AV valve or bicuspid valve Right AV valve or tricuspid valve It prevents back flow of blood from the RV to the RA (mitral valve) It prevents back flow of blood from the LV to the LA Pulmonary semilunar valves It prevents back flow of blood from the pulmonary trunk to the RV

Cusps Chordae tendineae Papillary muscle Trabeculae carneae Transverse section, superior view

Circumflex artery Left coronary artery Anterior I-V artery Posterior I-V artery Right coronary artery Right coronary artery Marginal arteries Left coronary artery Coronary sinus Great cardiac vein Circumflex artery Anterior interventricular artery Posterior interventricular artery Small cardiac vein Marginal artery Middle cardiac vein The Blood Supply to the Heart The Coronary Arteries

Atrioventricular bundle or bundle of His Right and left bundle branches Sinoatrial node (SA node) Atrioventricular node (AV node) Purkinje fibers The Conducting System It connects electrically the atria to the ventricles. They conduct the impulse to the Purkinje fibers. It establishes the heart rate (pacemaker). It delays the impulses to allow the atria to finish contracting before the ventricles start to contract. They conduct the impulse to the lateral walls of the ventricles allowing the contraction to spread from the apex to the base.

Impulse Conduction through the Heart SA node fires and atrial activation begin. Time 0 5 2 3 4 5 5 1 2 3 4 1 Stimulus spreads across the atrial surfaces and reaches the AV node. Elapsed time: 50 msec There is a 100 msec delay at the AV node. Atrial contraction begins. AV node fires. Elapsed time : 150 msec The impulse travels along the inter-ventricular septum within the AV bundle and the bundle branches to the Purkinje fibers. Elapsed time: 175 msec The impulse is distributed by Purkinje fibers and relayed through the ventricular myocardium. Atrial contraction is completed and ventricular contraction begins. Elapsed time: 225 msec

The Cardiac Cycle At the beginning of their contraction (systole) the ventricles contracts isovolumetrically (the pressure increases but the volume inside the ventricles does not changes). In the period of isovolumetric contraction, the ventricles contract and the pressure rises, but blood does not flow because all the valves are closed. Pressure Pressure

The Cardiac Cycle At the beginning of their contraction (systole) the ventricles contracts isovolumetrically (the pressure increases but the volume inside the ventricles does not changes). In the period of isovolumetric contraction, the ventricles contract and the pressure rises, but blood does not flow because all the valves are closed. Pressure Pressure Once pressure in the ventricles exceeds that in the arterial trunks (pulmonary and aortic), the semilunar valves open and blood flows into the pulmonary and aortic trunks. This point marks the beginning of the period of ventricular ejection.

(b) At the start of the atrial systole, the ventricles are already filled to about 70% of their normal capacity, due to passive blood flow. At the end of the atrial systole, each ventricle contains a maximum amount of130 mL of blood: End-diastolic volume (a) (c) In the period of isovolumetric contraction, the ventricles contract and the pressure rises, but blood does not flow because all the valves are closed. (d) (e) This point marks the beginning of the period of ventricular ejection.

(f) At the start of the atrial systole, the ventricles are already filled to about 70% of their normal capacity, due to passive blood flow. (a) Atrial Systole A small amount of blood (30 %) is forced to the ventricles Ventricular contraction closes the AV valves (first sound). Isometric contraction. Fist Phase: Ventricular Systole Pressure increases and semilunar valves open. Ventricular ejection. Second Phase: Pressure decreases in the ventricles and semilunar valves close (second sound). Early: Ventricular Diastole Atria are also in diastole. Passive blood flow fills the ventricles (70%). Late: Atrial Diastole Ventricles are also in diastole. Passive blood flow fills the ventricles (70%).

Electrocardiogram or ECG (EKG) It is the graphic recording of the electrical activity of the heart as it works

The Electrocardiogram R QRS complex +1 Depolarization of ventricles Depolarization of atria T P Repolarization of ventricles 0 Q S PQ segment ST segment It represents the time during which the ventricles contract and eject blood Millivolts

0.8 sec 0.5 sec 75 bpm Sinus Rhythm (normal) 120 bpm Tachycardia 1.4sec 1.4sec 0.5 sec 0.3 sec 1.4sec 46 bpm Bradycardia Arrhythmia Extrasystole Nodal Rhythm Ventricular fibrillation Heart block

QRS complex Depolarization of ventricles Depolarization of atria Repolarization of ventricles T P ST segment ATRIAL ATRIAL ATRIAL DIASTOLE VENTRICULAR VENTRICULAR VENTRICULAR SISTOLE DIASTOLE SISTOLE DIASTOLE DIASTOLE

End-Diastolic Volume (EDV) It is the volume of blood that each ventricle contains at the end of ventricular filling (about 130 mL). Stroke Volume (SV) It is the volume of blood that each ventricle ejects during ventricular ejection (about 70 - 80 mL). End-Systolic Volume (ESV) It is the volume of blood left behind in the ventricles after ventricular ejection. EDV – SV = (ESV) Ejection fraction It is the percentage of the end-diastolic volume (EDV) that is ejected (about 54%). Cardiac Output (CO) The amount of blood pumped by the left ventricle in one minute Cardiac Output (CO) = Stroke Volume (SV) x Heart Rate (HR) 75 bpm x 80 mL/beat = 6000 mL/min (6L/min)

Superior vena cava (to the right atrium) Aortic arch Ascending aorta S A node (pace maker) (from the left ventricle) Right auricle Left auricle (from the right ventricle) Pulmonary trunk Left coronary artery Right ventricle Left ventricle Right coronary artery Circumflex artery Anterior interventricular artery Marginal artery Anterior view

(to the left atrium) Right pulmonary veins Right auricle Left pulmonary veins Left auricle (to the left atrium) (to the right atrium) Inferior vena cava Great cardiac vein Right ventricle Left ventricle Coronary sinus Posterior cardiac vein Small cardiac vein Middle cardiac vein Posterior interventricular artery (branch of the right coronary artery) Posterior view

Internal Structures Superior vena cava Aortic arch Conducting system Ligamentum arteriosum S A node (pace maker) Pulmonary trunk Ascending aorta Orifices of coronary arteries Aortic semilunar valve AV node Right AV valve or tricuspid valve Left AV valve or bicuspid valve Chordae tendineae Atrioventricular bundle (of His) Papillary muscles Left bundle branch Right bundle branch Trabeculae carneae Purkinje fibers

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• Preferences

The Human Heart - PowerPoint PPT Presentation

The Human Heart

The human heart diagram of the heart chambers of the heart the heart has four chambers or parts. these are called: blood vessels veins are tubes which bring blood ... – powerpoint ppt presentation.

• The heart has four chambers or parts. These are called
• Veins are tubes which bring blood without oxygen into the heart.
• Arteries are tubes which take blood with oxygen away from the heart and bring it all around the body.
• Together they are called blood vessels.
• Blood without oxygen comes into the heart through a vein.
• It goes into the first chamber called the right atrium.
• It then goes through an opening called a valve into the right ventricle.
• From there it is pumped to the lungs to collect some oxygen.
• Blood with oxygen comes back to the heart from the lungs.
• It goes into the left atrium.
• It then goes through an opening called a valve into the left ventricle.
• From there it is pumped away from the heart and all around the body through a very special artery called the aorta.
• http//www.heartlibrary.com/heart-library-heart-an atomy.aspx
• Put your left hand out.
• Put out your middle and pointing finger on the right hand.
• Place them on your left wrist below your thumb and search for a beat. This is your pulse.
• The pulse tells us how quickly the heart is pumping blood around the body.
• It should beat about 70 times every minute.
• COUNT HOW MANY TIMES YOU FEEL YOUR PULSE BEAT IN ONE MINUTE.
• Record your answer.
• My pulse is _____ per minute.
• Jog on the spot for one minute.
• Now count how many times you feel your pulse beat in one minute.
• When I ran for 1 minute my pulse was _____ per
• Do jumping jacks for one minute.
• When I did jumping jacks for 1 minute my pulse was_______________ per minute.

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Cardiac cycle

Author: Lorenzo Crumbie, MBBS, BSc • Reviewer: Dimitrios Mytilinaios, MD, PhD Last reviewed: October 30, 2023 Reading time: 24 minutes

The cardiac cycle is defined as a sequence of alternating contraction and relaxation of the atria and ventricles in order to pump blood throughout the body. It starts at the beginning of one heartbeat and ends at the beginning of another. The process begins as early as the 4th gestational week when the heart first begins contracting. 

Each cardiac cycle has a diastolic phase (also called diastole ) where the heart chamber is in a state of relaxation and fills with blood that receives from the veins and a systolic phase (also called systole ) where the heart chambers are contracting and pumps the blood towards the periphery via the arteries. Both the atria and the ventricles undergo alternating states of systole and diastole. In other words, when the atria are in diastole, the ventricles are in systole and vice versa.

This article will discuss the phases of the cardiac cycle and the underlying physiological principles that govern the process. There will be a brief review of the conducting system of the heart , as well as discussion of the disorders that affect the cardiac cycle.

Conducting system of the heart

Atrial diastole, atrial systole, ventricular diastole, ventricular systole, aortic pressure, atrial pressure, ventricular pressure and volume , electrocardiogram (ecg or ekg), phonocardiogram (heart sounds), frank-starling mechanism, electrolyte imbalance, heart failure.

Myocardiocytes are unique cells found in the heart that are able to independently generate and spread electrical activity from one cell to another. They are able to communicate through gap junctions (points of permeability) at the intercalated discs (where cell walls meet). The communication is so efficient that the cells form a syncytium where ions can freely and rapidly flow from one cell to another. As a result of this network, the heart muscles undergo almost simultaneous contraction. 

There is an area of sub-specialized cells known as the sinuatrial node (SA node) . This area is located near the opening of the superior vena cava on the superior lateral wall of the right atrium. The SA node is able to contract faster than the rest of the heart tissue and as a result, it sets the pace of cardiac contraction. Therefore it is referred to as the pacemaker of the heart . The SA node is able to spread its impulse to the rest of the right and left atria through preferential conductive pathways. 

There is a secondary area of concentrated conductive tissue known as the atrioventricular node (AV node) that is located medial and posterior to the tricuspid valve . Like the SA node, the AV node also has autonomous properties and is able to generate an action potential . However, these cells are slower than those in the SA node and as a result, they act in response to activity from the SA node. There are preferential internodal pathways that exist for more efficient transmission of the impulse to the AV node. 

The AV node is connected to a network of fibers that run down the interventricular septum then through the walls of the ventricles. The initial segment of this pathway is called the bundle of His . The bundle of his then bifurcates into the left and right bundle branches . The left bundle branch also gives of left posterior branches , which carries impulses to the posterior aspect of the left ventricle. Both the left and right bundle branches give off numerous branches known as Purkinje fibers that supply the ventricular myocardium.

How well do you know the anatomy of the heart? Test yourself with this quiz.

Cardiac cycle phases

The events of the cardiac cycle, start with a spontaneous action potential in the sinus node as we described previously. This stimulus causes a series of events in the atria and the ventricles. All these events are “organized” in two phases: 

• diastole (when the heart fills with blood)
• and systole (when the heart pumps the blood)

During these two phases, many different events are observed and we will describe them in the following paragraphs. 

Atrial diastole is the very first event of the cardiac cycle. It occurs some milliseconds before the electrical signal from the SA node arrives at the atria. The atria function as conduits that facilitate the passage of blood into the ipsilateral ventricle. They also act as primers to pump residual blood into the ventricles. During atrial diastole, blood enters the right atrium through the superior and inferior vena cava and the left atrium via the pulmonary veins . In the early part of this phase, the atrioventricular valves are closed and blood pools in the atria. 

There comes a point when the pressure in the atrium is greater than the pressure in the ventricle of the same side. This pressure difference results in the opening of the atrioventricular valves, allowing blood to flow into the ventricle. 

The autonomous sinuatrial node initiates an action potential that is propagated throughout the atrial myocardium. The electrical depolarization results in simultaneous contraction of the atria, thus forcing any residual blood from the upper chambers into the lower chambers of the heart. The atrial contraction causes a further increase in atrial pressures. 

During the early stages of ventricular diastole , both the atrioventricular and semilunar valves are closed. During this phase, there is no change in the amount of blood in the ventricle, but there is a precipitous fall in the intraventricular pressure. This is known as isovolumetric relaxation . 

Do you want to simplify your learning of the cardiac cycle? Master the anatomy of the heart first by using our diagrams, quizzes and worksheets of the heart that teach, test and help you to consolidate the material.

Eventually, the ventricular pressure becomes less than the atrial pressure, and the atrioventricular valves open. This results in filling of the ventricles with blood, which is often referred to as the rapid filling of the ventricles . It accounts for most of the blood that is in the ventricle before it contracts. A small volume of blood flows directly into the ventricles from the venae cavae. Towards the end of ventricular diastole, any residual blood in the atria is pumped into the ventricle. The total volume of blood present in the ventricle at the end of diastole is called the end-diastolic volume or preload .

Ventricular systole refers to the period of contraction of the ventricles. The electrical impulse arrives at the atrioventricular node (AV node) shortly after the atria are depolarized. There is a small delay at the AV node, which allows the atria to complete contracting before the ventricles are depolarized. The action potential passes to the AV node, down the bundle of His , and subsequently to the left and right bundle branches (conductive fibers that travel through the interventricular septum and branches to supply the ventricles). These fibers carry the electrical impulses through their respective ventricular territories, leading to ventricular contraction .

As the ventricle begins to contract, the pressure exceeds that of the corresponding atrium, resulting in the closure of the atrioventricular valves. At the same time, the pressure is not sufficient to open the semilunar valves. Therefore, the ventricles are in a state of isovolumetric contraction – as there is no change in the overall volume (end-diastolic volume) in the ventricle. 

As the ventricular pressure exceeds the pressure in the outflow tract, the semilunar valves open, allowing blood to leave the ventricle. This is the ejection phase of the cardiac cycle. The amount of blood left in the ventricle at the end of systole is known as the end-systolic volume ( afterload , between 40 – 50 ml of blood). The amount of blood actually ejected from the ventricle is known as the stroke volume output . The ratio of the stroke volume output to the end-diastolic volume is called the ejection fraction and usually amounts to around 60%. 

The ventricles re-enter in a state of isovolumetric relaxation and the atria continue to fill. The process starts over and continues to repeat for as long as the individual is alive.

Take our custom quiz to test yourself on the structures that the blood passes throughout the cardiac cycle!

Wiggers Diagram

The American-born physiologist Dr. Carl J Wiggers has provided many health care students over the past 100 years with a unique tool to understand the cardiac cycle. The Wiggers diagram highlights the relationship between pressure and volume over time, along with the electrical activity of the heart. The diagram uses the left chambers of the heart to demonstrate:

• Ventricular pressure
• Ventricular volume
• Electrocardiogram (ECG)

The aortic pressure graph shows the change in pressure within the aorta throughout the cardiac cycle. The graph has a moderate incline followed by a notch , then a smaller incline . The graph ends with a gradual decline before starting over. 

The increase in ventricular pressure during systole causes the aortic valve to open. The pressure generated in the ventricle is then transmitted to the aorta . The walls of the aorta are able to dilate due to their high elasticity in order to accommodate the sudden, dramatic increase in pressure. These pressure changes are represented by the first and largest wave on the aortic pressure graph . 

At the end of systole, the left ventricle stops contracting but the aorta maintains relatively higher pressures. The sudden change in the pressure gradient results in a small backflow of blood into the left ventricle just before the aortic valves close. This is represented on the aortic pressure graph by a sharp decline or ‘ incisura ’ and then a sharp increase. The aortic pressure then gradually decreases throughout ventricular diastole until it reaches its resting pressure. 

This graph is similar to the pressure relationship between the right ventricle and the pulmonary artery . The main difference is that the pressure is significantly lower.

The atrial pressure wave shows the change in the atrial pressure during systole and diastole. There are three significant pressure changes represented by the letters a , v , and c . The pressure change generated as the atria fill with blood is represented by the ‘v’ wave towards the end of the atrial pressure wave. There is a slight decline in the atrial pressure that corresponds with the opening of the atrioventricular valve. This is followed by the ‘a’ wave which represents the contraction of the atria. The ‘a’ wave is followed by a downward slope as the atrioventricular valves close. This is followed by another increase labeled as the ‘c’ wave . This represents bulging of the atrioventricular valves into the atria during ventricular contraction.

The pressure and volume changes that occur in the ventricle is represented on two separate curves. However, they are best interpreted together. The ventricular pressure curve has two waves – an initial small wave followed by a return to the baseline pressure, then a significantly larger wave. The ventricular volume curve , however, has a mixture of sudden and gradual slopes and inclines throughout its cycle.

Consider the start of the ventricular volume curve at the beginning of diastole. Here, there is a residual volume of about 50 mL of blood left in the ventricle. At this point, the pressure curve is on a sharp decline during isovolumetric relaxation. Once the ventricular pressure is less than the atrial pressure, the atrioventricular valve opens. There is a rapid increase in the ventricular volume followed by a slow gradual increase (in-keeping with the passive filling phase). During this time, the ventricular pressure remains unchanged as the chamber is able to accommodate the increasing volume. 

The first increase in the ventricular pressure occurs as the atria contract to pump residual blood into the ventricle. This increase doesn’t last for a long time and the ventricular pressure soon returns to baseline. At this time more blood is being pumped into the ventricle, bringing it to its end-diastolic or preload volume. At the beginning of systole, the atrioventricular valves are closed and the ventricle is in isovolumetric contraction. So there is a sharp increase in pressure but the volume remains the same. Once the ventricular pressure overcomes the aortic pressure, the aortic valves open and there is a sudden fall in ventricular volume. As the volume decreases, the ventricular pressure begins to fall as well. Eventually, the ventricle stops contracting, re-enters the diastolic phase, and begins isovolumetric relaxation.

The electrocardiogram is a graphical representation of the electrical activity across the heart. It is comprised of a series of waves that represent depolarization and troughs that represent repolarization . If you need a refresher on the basic principles of the ECG, please refer to other articles on Kenhub that covers this material.

There is a lag between the depolarization of the myocardiocytes and the actual contraction of the muscles. As a result, the waves of the ECG will precede the waves of the pressure curves (which are caused by actual contraction of the heart muscle). The ‘P’ wave which represents atrial depolarization precedes the ‘a’ wave of the atrial pressure graph. The ‘QRS’ complex represents ventricular depolarization, which causes the ventricles to contract. The large wave of the ventricular pressure graph begins shortly after the ‘QRS’ wave. The ‘T’ wave of the ECG represents a time of ventricular repolarization and subsequent relaxation. Therefore, this wave starts toward the end of systole.

The phonocardiogram represents the heart sounds throughout the cardiac cycle. These heart sounds are which are appreciated during auscultation represent the effects of the heart valves as they close. They are commonly referred to as the “lub” and “dub” sounds. 

The first heart sound or S1 or the “lub” sound is caused by the closure of the atrioventricular valves. This occurs at the beginning of ventricular systole. It can be graphically represented at the point after the first ventricular pressure wave. This coincides with the ‘a’ wave of the atrial pressure wave, and the ‘R’ wave of the ECG. The second heart sound or S2 or the “dub” sound is caused by the closure of the semilunar valves. This occurs at the beginning of diastole, during the isovolumetric relaxation phase. It coincides with the ‘incisura’ of the aortic pressure curve and the terminal end of the ‘T’ wave of the ECG. 

It is not abnormal to hear a third heart sound or S3 at times. This is usually caused by a sudden rush of blood into the ventricles from the atria. It is, therefore, most commonly a mid-diastolic sound that occurs after S2.

The heart has a remarkable capacity to accommodate an increased volume of blood coming into the heart. In fact, increasing the end-diastolic volume also results in an increase in cardiac output. This principle has been described by two renowned physiologists, and therefore referred to as the Frank-Starling mechanism of the heart . The underlying principle is that the heart will pump all the blood that returns to it by way of the veins, within physiological limits .

When there is an increase in ventricular preload, the ventricle is distended and by extension, the myocardiocytes are also stretched. This distension brings the actin and myosin components of the muscle fiber to a more optimal degree. Consequently, the muscle fibers will contract with a greater force in order to pump the extra blood. Note, however, that this principle is only valid up to an optimal point. Any further distension beyond that point will dissociate the actin-myosin complex, making it difficult for a contraction to occur.

Disorders affecting the cardiac cycle

The cardiac cycle is a highly coordinated process that keeps blood moving throughout the body. It is heavily dependent on tight choreography of events and any disruption of these events can be detrimental. Some of these problems can occur acutely (electrolyte imbalances) or may take years to develop (heart failure).

Electrolytes are important ions found both within cells and in the extracellular fluid. They are particularly important in generating and propagating action potentials. One particularly important ion as it pertains to activation of muscle action potentials is potassium (K+) . Potassium ions are important in altering the cells’ resting membrane potential . Significant increase or decrease in the amount of these ions in the extracellular fluid (hyperkalemia and hypokalemia) can be fatal.

Hyperkalemia

A build-up of potassium ions in the blood is referred to as hyperkalemia . The presence of more potassium ions outside the cells changes the electrical gradient across the cell membrane. As a result, the cell membrane becomes less negative and is initially more easily excitable. However, as the potassium concentration increases more, fewer sodium ion channels are recruited during depolarization. This results in a decline in the influx of sodium ions into the muscle cells and consequently a slower generation of action potential and eventually a reduction in the conduction of the impulse. Hyperkalemia can also cause AV nodal block , which impairs the passage of the depolarization wave to the ventricles.

Hyperkalemia is most detrimental when it develops over a short period of time. While some patients may remain asymptomatic, others may complain of chest pain, shortness of breath, muscle paralysis, and palpitations. There are classic signs on the ECG tracing that are highly suggestive of hyperkalemia:

• The T waves become tall and peaked because of the sudden repolarization
• The P wave widens and becomes flattened due to paralysis of the atria
• The PR interval widens due to a delay in the conduction from the SAN to the AVN
• The QRS complex becomes wider and may eventually blend with the T wave. This results from the AV nodal block.

Essentially, the heart becomes flaccid, dilated, and slow. This decreased contractility results in a decrease in the forward movement of blood, which can be fatal.

Hypokalemia

A significant fall in the number of potassium ions in the blood is referred to as hypokalemia . Hypokalemia has the opposite effect on the membrane potential than hyperkalemia. The decrease in extracellular potassium causes the cellular membrane to become more negative, resulting in an increase in the electrical gradient across the membrane. While this makes it more difficult for other cells to depolarize, an increased electrical gradient causes faster depolarization of myocardiocytes. This effect is most profound at the Purkinje fibers, which are most sensitive to changes in potassium concentration.

The increased excitability at points other than the pacemaker site predisposes the heart to develop ectopic heartbeats . These may lead to uncoordinated contraction of the ventricles and varying types of ventricular arrhythmias . 

Additionally, a dramatic fall in the serum potassium level can also cause inhibition of some potassium ion channels. This impairs the transportation of potassium from the intracellular to the extracellular space. Consequently, ventricular repolarization is impaired and the cell may become depolarized prematurely . This can cause reentrant rhythms and other arrhythmias to occur. These repolarization abnormalities can be appreciated on ECG as:

• Flattening and inversion of the T wave
• More prominent U waves 
• Depression of the ST segment
• Prolonged QT intervals

The rapid, irregular heart is no longer effective in propelling blood forward through the circulatory system. 

Heart failure is a syndrome that refers to the inability of the heart to move blood forward through the circulatory system. This is often the common final pathway of many different forms of heart failure. Heart failure may occur as a result of reduced contractility of the ventricles or increased resistance to blood flow. Both these factors are the hallmark features of systolic dysfunction . On the other hand, the ventricles may not relax properly or the walls may be too stiff, thus impairing cardiac filling. These features are typical of diastolic dysfunction . 

Heart failure can be further subdivided into right and left heart failure depending on the symptoms and signs present. Patients with left heart failure often have a history of chronic, uncontrolled (or poorly controlled) systemic hypertension, valvular insufficiency, or dilated cardiomyopathy. Patients may experience:

• Shortness of breath
• Paroxysmal nocturnal dyspnea
• Coughing with or without rusty sputum

In contrast, patients with right heart failure may have a history of pulmonary hypertension, tricuspid insufficiency, pulmonary stenosis, or left heart failure (referred to as left to right heart failure). In the absence of left heart failure, symptoms of right heart failure include:

• Peripheral edema
• Sacral edema
• Hepatosplenomegaly
• Weight loss (cardiac cachexia)

Although there are many compensatory mechanisms that mitigate the progression of heart failure, the process – once it has begun – cannot be reversed. Patients may continue to compensate for the impaired cardiac function; they may still have acute decompensation following illness or noncompliance with medication or dietary restriction.

References:

• Guyton, A., & Hall, J. (2007). Textbook of medical physiology (11th ed.). India: Elsevier Saunders.
• Mitchell, J., & Wang, J. (2014). Expanding application of the Wiggers diagram to teach cardiovascular physiology. Advances In Physiology Education, 38(2), 170-175. doi: 10.1152/advan.00123.2013
• Netter, F. (2014). Atlas of Human Anatomy (6th ed.). Philadelphia, PA: Saunders.
• Pollock, J., & Makaryus, A. (2019). Physiology, Cardiac Cycle. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK459327/
• Standring, S., & Gray, H. (2008). Gray's anatomy (42nd ed.). Edinburgh: Churchill Livingstone/Elsevier.

Illustrators:

• Heart diagram (anterior view) - Yousun Koh 
• Heart diagram (posterior view) - Yousun Koh 
• Wiggers Diagram - adh30 revised work by DanielChangMD who revised original work of DestinyQx; Redrawn as SVG by xavax [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
• Electrocardioagram features - Created by Agateller (Anthony Atkielski), converted to svg by atom. [Public domain]

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