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How does an electrical impulse travel through the heart’s conduction system?

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Illustration of a human heart cross-section showing four chambers-left and right atria and ventricles-with labeled major blood vessels. An inset highlights cardiac muscle tissue, showing myocytes and intercalated disks. — human cardiovascular system The human heart is both a pump and a muscle. Its four chambers move blood efficiently, while cardiac muscle cells joined by intercalated disks synchronize each contraction.

The heart’s rhythmic contraction is governed by an internal conduction system that ensures the coordinated pumping of blood. This process begins in the sinoatrial (SA) node, a cluster of specialized pacemaker cells located in the right atrium.12

These cells possess the unique ability to spontaneously depolarize, generating an electrical impulse that sets the heart's pace. The signal travels through the heart via the following pathway:23

Atrial Propagation: The impulse spreads from the SA node across the atria, causing them to contract.13
Atrioventricular (AV) Node: The signal reaches the AV node, which acts as a relay point.23
Ventricular Conduction: From the AV node, the impulse is transmitted rapidly through the bundles of His and the Purkinje system.23
Ventricular Contraction: The signal disperses into the ventricular muscle cells, triggering a coordinated contraction that pumps blood to the lungs and the rest of the body.13

This propagation is facilitated by low-resistance pathways between cells, such as intercalated disks, and is driven by the movement of ions like sodium, potassium, and calcium across cell membranes.23