The myocardium of the heart can generate its own electrical impulse, an ability called automaticity.

The Sinoatrial node (SA node) in the right atrium works like an internal pacemaker. This node generates electrical impulses at a rate of 60-100 times per minute. Each impulse travels through internodal pathways in the right and left atria and depolarizes the myocardial cells, causing the muscle in the atrium to contract.

From the SA node in the atria, an electrical impulse travels to the atrioventricular node (AV node). Here, it experiences a strategic delay, then releases to go through the bundle of His. It then ultimately travels to the Purkinje fibers, which wrap around the ventricles to complete the cycle of a single heartbeat.

The delay in the AV node allows the ventricles to beat independently of the atria so the heart can operate in a double-pump action.

The ventricular contraction pushes the oxygenated blood to the extremities of the body.

If the SA node, the primary impulse generator, does not work properly, the AV node can send its own impulses instead. However, it generates impulses at a slower pace—40-60 beats a minute. The AV node’s impulse travels through the bundle of His and Purkinje fibers in the same way the SA node’s impulse does.

The bundle of His is the only route of electrical transmission that travels between the atria and the ventricles.

If neither the SA or AV node produces impulses properly, the Purkinje fibers will generate the impulse. But it produces the impulses at an even slower rate—15-40 beats a minute. This rate is usually too slow to oxygenate cells within the body.