What structure is considered the pacemaker of the heart?

The sinoatrial (SA) node is referred to as the pacemaker of the heart because it initiates the electrical impulses that dictate the heart's rhythm and rate. Located in the right atrium, the SA node generates spontaneous action potentials at a rate that establishes the baseline heart rate under normal physiological conditions.

These electrical signals travel through the atria, causing them to contract and push blood into the ventricles, and then to the atrioventricular (AV) node, which helps to relay the impulse to the ventricles. The influence of the SA node is modulated by the autonomic nervous system, but it inherently possesses the highest rate of automaticity compared to any other component of the conduction system, which includes the AV node and the bundle of His.

Other structures, while integral to cardiac function, do not have the same role as the SA node in initiating the heart's rhythm. The AV node, for instance, acts as a gatekeeper that slows down the conduction from the atria to the ventricles, but it does not spontaneously generate impulses at the same rapid frequency. The aorta is a major artery, not involved in the pacemaking function, and the pectinate muscles are primarily structural components in the atrial