Assertion: The normal heart rate is $75\text{beats}/\text{min}$ and the cardiac cycle is $0.8sec$. ​

Reason: Cardiac cycle is inversely proportional to the heart rate.

1. If both assertion and reason are false​
2. If an assertion is true but the reason is false​
3. If both assertion and reason are true then the reason is not the correct explanation of assertion​
4. If both assertion and reason are true and the reason is the correct explanation of assertion.​

The correct option is D If both assertion and reason are true and the reason is the correct explanation of assertion.​
Correct option: (A) If both assertion and reason are true and the reason is the correct explanation of assertion.

The normal heartbeat is $75$ beats per minute, which means a complete cardiac cycle in one minute.​

One complete cardiac cycle takes $0.8$ seconds.​

The ventricle of the heart pumps approximately $70ml$ of blood; it is called stock volume during a cardiac cycle.