The sino-atrial node (SA node) is located in the right atrium of the heart. The other popular name of the SA node is the sinus node. It is the impulse generating tissue or precisely speaking a natural pacemaker. It generates the sound of the heart beat. The AV node (atrio-ventricular node) is located between the atria and the ventricles of the heart. The AV node generates the impulses from the atria to the ventricles. The AV node is also the natural pacemaker of the heart. The SA node is the primary and the AV node is the secondary pacemaker of the heart.