A specialised nodal tissue embedded in the lower corner of the right atrium, close to Atrio-ventricular septum, delays the spreading of impulses to heart apex for about 0.1 sec. The delay allows

Because the spreading of impulses through the AV node is delayed, it takes about 0.1 seconds for the action potentials to reach the ventricle from the atria. This allows the atria to empty completely and the ventricles to contract only after the atrial systole is completed (and ventricles are completely filled).