Heart; conduction system. 1. SA node. 2. AV node. 3. Bundle of His. 8. Septum
Human heart during an autopsy
3D rendering showing thick myocardium within the heart wall.
Overview of the system of electrical conduction which maintains the rhythmical contraction of the heart
Computer-generated animation of a beating human heart
The swirling musculature of the heart ensures effective pumping of blood.
The human heart is in the middle of the thorax, with its apex pointing to the left.
Cardiac muscle
Principle of ECG formation. Note that the red lines represent the depolarization wave, not bloodflow.
Heart being dissected showing right and left ventricles, from above
Illustration of a cardiac muscle cell.
Different wave shapes generated by different parts of the heart's action potential
Frontal section showing papillary muscles attached to the tricuspid valve on the right and to the mitral valve on the left via chordae tendineae.
Intercalated discs are part of the cardiac muscle cell sarcolemma and they contain gap junctions and desmosomes.
Layers of the heart wall, including visceral and parietal pericardium
Dog cardiac muscle (400X)
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 electrical conduction system of the heart transmits signals generated usually by the sinoatrial node in the heart to cause contraction of the heart muscle.

- Electrical conduction system of the heart

It is involuntary, striated muscle that constitutes the main tissue of the wall of the heart.

- Cardiac muscle

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

- Heart

These generate a current that causes the heart to contract, traveling through the atrioventricular node and along the conduction system of the heart.

- Heart

Other potential roles for fibroblasts include electrical insulation of the cardiac conduction system, and the ability to transform into other cell types including cardiomyocytes and adipocytes.

- Cardiac muscle

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Sinoatrial node shown at 1. The rest of the conduction system of the heart is shown in blue.

Sinoatrial node

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Sinoatrial node shown at 1. The rest of the conduction system of the heart is shown in blue.
Figure 2: Low magnification stained image of the SA node (center-right on image) and its surrounding tissue. The SA node surrounds the sinoatrial nodal artery, seen as the open lumen. Cardiac muscle cells of the right atrium can be seen to the left of the node, and fat tissue to the right.
Figure 3: Sinoatrial node action potential waveform, outlining major ion currents involved (downward deflection indicates ions moving into the cell, upwards deflection indicates ions flowing out of the cell).
Schematic representation of the atrioventricular bundle

The sinoatrial node (also known as the sinuatrial node, SA node or sinus node) is a group of cells known as pacemaker cells, located in the wall of the right atrium of the heart.

These cells can produce an electrical impulse (action potential) that travels through the electrical conduction system of the heart, causing it to contract.

The main role of a sinoatrial node cell is to initiate action potentials of the heart that can pass through cardiac muscle cells and cause contraction.

Isolated heart conduction system showing Purkinje fibers

Purkinje fibers

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Isolated heart conduction system showing Purkinje fibers
Purkinje fiber just beneath the endocardium.

The Purkinje fibers (often incorrectly ; Purkinje tissue or subendocardial branches) are located in the inner ventricular walls of the heart, just beneath the endocardium in a space called the subendocardium.

They are larger than cardiomyocytes with fewer myofibrils and many mitochondria.

Purkinje fibers allow the heart's conduction system to create synchronized contractions of its ventricles, and are essential for maintaining a consistent heart rhythm.

Image showing the cardiac pacemaker or SA node, the normal pacemaker within the electrical conduction system of the heart.

Cardiac pacemaker

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Image showing the cardiac pacemaker or SA node, the normal pacemaker within the electrical conduction system of the heart.
Schematic representation of the sinoatrial node and the atrioventricular bundle of His. The location of the SA node is shown in blue. The bundle, represented in red, originates near the orifice of the coronary sinus, undergoes slight enlargement to form the AV node. The AV node tapers down into the bundle of HIS, which passes into the ventricular septum and divides into two bundle branches, the left and right bundles. The ultimate distribution cannot be completely shown in this diagram.

The contraction of cardiac muscle (heart muscle) in all animals is initiated by electrical impulses known as action potentials.

Sometimes an ectopic pacemaker sets the pace, if the SA node is damaged or if the electrical conduction system of the heart has problems.