(a) What is meant by 'heart beat'? What is the usual heart beat rate at rest?(b) What change occurs in heart beats if a person runs for a while? Why?

(a) Heart beat: One complete contraction and relaxation of the heart is called a heart beat. The usual heartbeat rate at rest in a healthy person is 72 times /minute.

(b) The heart beats faster when a person runs for a while as the body needs more energy under these conditions.