Final answer:
The natural pacemaker of the heart, which regulates the heartbeat, is the sinoatrial (SA) node. It initiates the sinus rhythm, or normal electrical pattern followed by contraction of the heart.
Step-by-step explanation:
The natural pacemaker of the heart, which regulates the heartbeat, is the sinoatrial (SA) node. It is a specialized clump of myocardial conducting cells located in the right atrium. The SA node has the highest inherent rate of depolarization and initiates the sinus rhythm, or normal electrical pattern, that leads to contraction of the heart.