Also known as the AV node. A major part of the electrical system in the heart that acts as a gateway between the atria and the ventricles. An electrical signal generated by the sinoatrial node (the heart's natural pacemaker) moves through the heart until it reaches the atrioventricular node, a cluster of cells at the bottom of the right atrium. The AV node delays the signal before it is passed to the ventricles. This lets the atria fully contract before the ventricles contract.