Final answer:
The sinoatrial (SA) node is responsible for setting the basic rhythm of the heartbeat by functioning as the heart's natural pacemaker.
Step-by-step explanation:
The basic rhythm of the heartbeat is set by the sinoatrial (SA) node. This area of specialized cells, located in the right atrium of the heart, functions as the natural pacemaker, initiating the sinus rhythm that governs the contractions of the heart. The electrical signals originating from the SA node cause the atria to contract and then travel to the atrioventricular (AV) node, after which they reach the ventricles, culminating in their contraction.