What component of the conduction system is referred to as the pacemaker of the heart?

A. Atrioventricular (AV) node: The AV node conducts electrical signals from the atria to the ventricles, but it is not the pacemaker of the heart. B. Bundle branches: The bundle branches transmit the electrical impulses to the ventricles but are not the primary pacemaker. C. Bundle of His: The Bundle of His conducts electrical signals from the AV node to the bundle branches and ventricles but does not act as the pacemaker. D. Sinoatrial (SA) node: The SA node, located in the right atrium, is the primary pacemaker of the heart, initiating electrical impulses that regulate heart rhythm.