Write the feature that distinguishes between the two: Sino-atrial node and Atrio-ventricular node.

(N/A) $SA$ node: It is a specialized patch of nodal tissue present in the right upper corner of the right atrium. It acts as the natural pacemaker of the heart as it initiates the rhythmic contractile activity of the heart.
$AV$ node: It is a specialized mass of cardiac tissue located in the lower left corner of the right atrium close to the atrio-ventricular septum. It receives the action potential from the $SA$ node and delays it slightly before transmitting it to the bundle of His.