In higher vertebrates,$SA-$node helps in

What is a pacemaker?

All the components of the conducting system can generate an action potential for the contraction of heart muscle,but the Sinoatrial node acts as the pacemaker because

The number of action potentials generated by the sino-atrial node $(SAN)$ in a healthy human is $ . . . . . . $ per minute.

Where are valves found in the circulatory system?

The two auricles are demarcated externally from the ventricles by an irregular groove called: