Interior of right side of heart
Illustration depicting the layers of the heart wall including the innermost endocardium
Histology of the endocardium and subendocardium.

Innermost layer of tissue that lines the chambers of the heart.

- Endocardium

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Muscular organ in most animals that pumps blood through the blood vessels of the circulatory system.

Human heart during an autopsy
Computer-generated animation of a beating human heart
The human heart is in the middle of the thorax, with its apex pointing to the left.
Heart being dissected showing right and left ventricles, from above
Frontal section showing papillary muscles attached to the tricuspid valve on the right and to the mitral valve on the left via chordae tendineae.
Layers of the heart wall, including visceral and parietal pericardium
The swirling pattern of myocardium helps the heart pump effectively
Arterial supply to the heart (red), with other areas labelled (blue).
Autonomic innervation of the heart
Development of the human heart during the first eight weeks (top) and the formation of the heart chambers (bottom). In this figure, the blue and red colors represent blood inflow and outflow (not venous and arterial blood). Initially, all venous blood flows from the tail/atria to the ventricles/head, a very different pattern from that of an adult.
Blood flow through the valves
The cardiac cycle as correlated to the ECG
The x-axis reflects time with a recording of the heart sounds. The y-axis represents pressure.
Transmission of a cardiac action potential through the heart's conduction system
Conduction system of the heart
The prepotential is due to a slow influx of sodium ions until the threshold is reached followed by a rapid depolarization and repolarization. The prepotential accounts for the membrane reaching threshold and initiates the spontaneous depolarization and contraction of the cell; there is no resting potential.
3D echocardiogram showing the mitral valve (right), tricuspid and mitral valves (top left) and aortic valve (top right).
The closure of the heart valves causes the heart sounds.
Cardiac cycle shown against ECG
Heart and its blood vessels, by Leonardo da Vinci, 15th century
Animated heart
Elize Ryd making a heart sign at a concert in 2018
The tube-like heart (green) of the mosquito Anopheles gambiae extends horizontally across the body, interlinked with the diamond-shaped wing muscles (also green) and surrounded by pericardial cells (red). Blue depicts cell nuclei.
Basic arthropod body structure – heart shown in red
The human heart viewed from the front
The human heart viewed from behind
The coronary circulation
The human heart viewed from the front and from behind
Frontal section of the human heart
An anatomical specimen of the heart
Heart illustration with circulatory system
Animated Heart 3d Model Rendered in Computer

The wall of the heart is made up of three layers: epicardium, myocardium, and endocardium.

Heart valve

One-way valve that allows blood to flow in one direction through the chambers of the heart.

Valves of the heart in motion, the front wall of the heart is removed in this image.
Structure of the heart valves
Blood flow through the valves
3D - loop of a heart viewed from the apex, with the apical part of the ventricles removed and the mitral valve clearly visible. Due to missing data, the leaflets of the tricuspid and aortic valves are not clearly visible, but the openings are; the pulmonary valve is not visible. On the left are two standard 2D views (taken from the 3D dataset) showing tricuspid and mitral valves (above) and aortal valve (below).
Wiggers diagram, showing various events during a cardiac cycle, with closures and openings of the aortic and mitral marked in the pressure curves.
This is further explanation of the echocardiogram above. MV: Mitral valve, TV: Tricuspid valve, AV: Aortic valve, Septum: Interventricular septum. Continuous lines demarcate septum and free wall seen in echocardiogram, dotted line is a suggestion of where the free wall of the right ventricle should be. The red line represents where the upper left loop in the echocardiogram transects the 3D-loop, the blue line represents the lower loop.
Illustration of the valves of the heart when the ventricles are contracting.

The heart valves and the chambers are lined with endocardium.


Double-walled sac containing the heart and the roots of the great vessels.

Walls of the heart, showing pericardium at right.
A transverse section of the thorax, showing the contents of the middle and the posterior mediastinum. The pleural cavity and the pericardial cavity are exaggerated since normally there is no space between the pleurae or between the pericardium and heart. Pericardium is also known as cardiac epidermis.
The pericardial cavity in this image is labeled d and is part of the inferior mediastium. Here we can see its relation to the superior mediastinum a, the pleural cavities c, and the diaphragm e.
3D still showing the pericardium layer.
Fibrous pericardium

The visceral serous pericardium, also known as the epicardium, covers the myocardium of the heart and can be considered its serosa. It is largely made of a mesothelium overlying some elastin-rich loose connective tissue. During ventricular contraction, the wave of depolarization moves from the endocardial to the epicardial surface.

Cardiac muscle

One of three types of vertebrate muscle tissue, with the other two being skeletal muscle and smooth muscle.

3D rendering showing thick myocardium within the heart wall.
The swirling musculature of the heart ensures effective pumping of blood.
Cardiac muscle
Illustration of a cardiac muscle cell.
Intercalated discs are part of the cardiac muscle cell sarcolemma and they contain gap junctions and desmosomes.
Dog cardiac muscle (400X)

The cardiac muscle (myocardium) forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium), with blood supplied via the coronary circulation.


Bartonella henselae bacilli in cardiac valve of a patient with blood culture-negative endocarditis. The bacilli appear as black granulations.

Endocarditis is an inflammation of the inner layer of the heart, the endocardium.


Single layer of squamous endothelial cells that line the interior surface of blood vessels, and lymphatic vessels.

Diagram showing the location of endothelial cells
Endothelium lines the inner wall of vessels, shown here.
Microscopic view showing endothelium (at top) inside the heart.

Endothelium of the interior surfaces of the heart chambers is called endocardium.

Myocardial infarction

A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle.

A myocardial infarction occurs when an atherosclerotic plaque slowly builds up in the inner lining of a coronary artery and then suddenly ruptures, causing catastrophic thrombus formation, totally occluding the artery and preventing blood flow downstream.
Cross section showing anterior left ventricle wall infarction
Diagram showing the blood supply to the heart by the two major blood vessels, the left and right coronary arteries (labelled LCA and RCA). A myocardial infarction (2) has occurred with blockage of a branch of the left coronary artery (1).
A 12-lead ECG showing an inferior STEMI due to reduced perfusion through the right coronary artery. Elevation of the ST segment can be seen in leads II, III and aVF.
ECG : AMI with ST elevation in V2-4
Inserting a stent to widen the artery.

Cells in the area with the worst blood supply, just below the inner surface of the heart (endocardium), are most susceptible to damage.

Cardiac neural crest

Neural crest cells are multipotent cells required for the development of cells, tissues and organ systems.

Migration of cardiac neural crest cells. CNCCs begin as part of the neural crest and become more specialized after reaching their final destination.
A comparison between normal development and common abnormalities that arises during cardiac neural crest differentiation

The CNCCs interact with the cardiogenic mesoderm cells of the primary and secondary heart fields, which are derived from the cardiac crescent and will give rise to the endocardium, myocardium, and epicardium.

Cardiovascular disease

Class of diseases that involve the heart or blood vessels.

Micrograph of a heart with fibrosis (yellow) and amyloidosis (brown). Movat's stain.
Calcified heart of an older woman with cardiomegaly
Density-Dependent Colour Scanning Electron Micrograph SEM (DDC-SEM) of cardiovascular calcification, showing in orange calcium phosphate spherical particles (denser material) and, in green, the extracellular matrix (less dense material)
Cardiovascular diseases deaths per million persons in 2012

Endocarditis – inflammation of the inner layer of the heart, the endocardium. The structures most commonly involved are the heart valves.

Coronary arteries

The coronary arteries are the arterial blood vessels of coronary circulation, which transport oxygenated blood to the heart muscle.

Coronary arteries (labeled in red text) and other major landmarks (in blue text)
heart attack

These categories are called epicardial (above the epicardium, or the outermost tissue of the heart) and microvascular (close to the endocardium, or the innermost tissue of the heart).