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

(a) Heartbeat is the sound produced when there is contraction and relaxation of the heart. At rest, the human heart usually beats 70 to 72 times per minute.

(b) A person's heart beats faster after running for a while or when a person is strained physically. After, the physical strain the person needs more oxygen. Hence the heart pumps faster.