Question

Regulation of heart beat in mammals is due to -

• A. The presence of excess of oxygen in blood
• B. The presence of pacemaker in the heart
• C. The volume of blood in the circulatory system
• D. The presence of thyroxine in blood

Answer 1

The correct option is B The presence of pacemaker in the heart

Answer: (d)

Sino-atrial node (SAN) can generate the maximum number of action potentials, which are $70-75{\text{min}}^{–1}$, and is responsible for initiating and maintaining the rhythmic contractile activity of the heart.
Therefore, it is called the natural pacemaker of heart. This helps in regulation of heartbeat.