Sino-atrial node is present in the

Sino-atrial node (SAN) is a patch of nodal tissue is present in the right upper corner of the right atriumAtrio-ventricular node (AVN) is another mass of nodal tissue is seen in the lower left corner of the right atrium close to the atrio-ventricular septum.The nodal musculature has the ability to generate action potentials without any external stimuli, i.e., it is autoexcitable. However, the number of action potentials that could be generated in a minute vary at different parts of the nodal system. The SAN can generate the maximum number of action potentials, i.e., 70-75 min–1, and is responsible for initiating and maintaining the rhythmic contractile activity of the heart. Therefore, it is called the pacemaker.