The number of action potentials generated by sino-arterial node...

The sino-atrial node (SAN) is a specialised patch of cardiac musculature present in the right upper corner of the right atrium.

It has the ability to generate action potentials without any external stimuli, making it autoexcitable.

The SAN can generate the maximum number of action potentials, which is $70-75$ per minute in a healthy human.

This rate of action potential generation is responsible for initiating and maintaining the rhythmic contractile activity of the heart, which is why the SAN is called the pacemaker. Consequently, the normal human heart beats $70-75$ times per minute (average $72$ beats per minute).