Which structure acts as the natural pacemaker of the heart?

The sinoatrial (SA) node is known as the natural pacemaker of the heart because it generates electrical impulses that initiate the heartbeat. Located in the right atrium, the SA node sets the rhythm for the rest of the heart by determining the rate and timing of contractions. It sends out electrical signals that cause the atria to contract and push blood into the ventricles. This activity is crucial for maintaining an effective heart rhythm and synchronizing the contractions of the heart chambers.

The other structures mentioned play important roles in the cardiac conduction system but do not serve as the primary pacemaker. The atrioventricular (AV) node does receive impulses from the SA node and helps to delay them before transmitting to the ventricles, ensuring that the atria contract before the ventricles. The Bundle of His and Purkinje fibers are involved in the conduction of impulses through the ventricles but are subordinate to the SA node in initiating the heartbeat.