Which heart structure is responsible for rhythmically initiating heartbeats?

The sinoatrial node, often referred to as the SA node, is the primary pacemaker of the heart. It is located in the right atrium and is responsible for generating electrical impulses that initiate each heartbeat. These impulses spread through the atria, causing them to contract and push blood into the ventricles. The SA node's rhythmic firing is what sets the pace for the entire heart, making it key to maintaining a regular heart rhythm.

In contrast, other heart structures play different roles. The atrioventricular node acts as a gateway between the atria and ventricles, delaying the impulse slightly to ensure that the ventricles fill with blood before contracting. Purkinje fibers are specialized fibers that distribute the electrical impulse quickly throughout the ventricles, facilitating their contraction. While cardiac muscle tissue does contract to pump blood, it does not initiate the heartbeat; rather, it responds to the impulses generated by the SA node.