1. Atrioventricular node definition, a small mass of muscular fibers at the base of the wall between the atria, conducting impulses received from the sinoatrial node by way of the Atrioventricular bundles and, under certain conditions, functioning for the sinoatrial node as pacemaker of the heart

2. Because the sinoatrial node is responsible for the rest of the heart's electrical activity, it is sometimes called the primary pacemaker.