Which structure in the heart is known as the pacemaker?

The sinoatrial (SA) node is referred to as the pacemaker of the heart because it is responsible for initiating and regulating the electrical impulses that dictate the heartbeat. This node is located in the right atrium and generates electrical signals that cause the atria to contract, effectively pumping blood into the ventricles. As the primary pacemaker, the SA node sets the pace for the heart's rhythm, typically firing at a rate of 60 to 100 beats per minute in a resting individual.

The SA node's ability to autonomously generate impulses is crucial for maintaining a consistent heart rate and ensuring that the heart operates effectively as a pump. Signals from the SA node then travel to the atrioventricular (AV) node, which conducts impulses to the ventricles, but it does not act as the initial pacemaker of the heart. Other structures such as the Bundle of His and Purkinje fibers are essential for the conduction pathway but primarily play supportive roles in transmitting impulses after they are generated by the SA node. Therefore, the SA node's role as the primary initiator of heart rhythm justifies its title as the pacemaker.