The sinoatrial node is the impulse-generating pacemaker of the heart located in the right atrium of the heart. In other words - it makes your heart beat.
Note that if the SA node fails for some reason, other nodes are ready to take over
Each heartbeat begins with an action potential generated at the sinoatrial node or simple call the SAnode.
The SA node normally functions as the pacemaker for the entire heart because its intrinsic rate is the fastest in the system. From the SA node, impulses spread out over the atria, causing them to contract.