The sinoatrial node, often called the SA node, is a small cluster of cells located in the right atrium of the heart. It acts as the heart's natural pacemaker, generating electrical impulses that initiate each heartbeat. These impulses spread through the heart, causing the atria to contract and pump blood into the ventricles. The SA node plays a crucial role in maintaining a regular heart rhythm. It responds to the body's needs, increasing the heart rate during exercise or stress and slowing it down during rest. This ability to adapt helps ensure that the body receives the right amount of blood and oxygen at all times.