Which structure in the heart is known as the natural pacemaker?

The structure known as the natural pacemaker of the heart is the Sinoatrial (SA) node. This is a specialized group of cells located in the right atrium that initiates the electrical impulses responsible for the heart's rhythm. The SA node generates electrical signals at regular intervals, which then propagate through the atria, causing them to contract and pump blood into the ventricles. It is this ability to spontaneously depolarize that gives the SA node its role as the primary pacemaker.

The importance of the SA node lies in its ability to set the pace for the heart's activity, regulating the heart rate in response to the body’s needs, such as during rest or exercise. This central function in coordinating cardiac rhythm is why it is often referred to as the "natural pacemaker." Other structures in the heart, such as the AV node and the Bundle of His, play important roles in the conduction of impulses but do not have the same capacity for initiating electrical activity independently.