Heartbeats vary depending on various factors such as age, physical state, and stimuli. A child has a smaller heart and therefore their heart needs to beat faster in order to pump the proper amount of blood. The heartbeat rate for infants is 120 per minute, for a child is about 90 times per minute, and for a person over age 18 is about 70 times per minute. A physically fit person has a lower heart rate as compared to an inactive person. Stimuli resulting in stress, fear or excitement will result in a rapid heartbeat.
Nerves connected to the heart regulate the speed with which the cardiac muscle contracts.
Interestingly, in an average lifetime, the heart continuously beats more than 2.5 billion times. People with heart disease produce irregular sounds that are emitted for each heartbeat. A pacemaker is an electrical device that is used to stimulate regular beating of the heart for people who have heart disease. Frequency is denoted as the number of times a regularly recurring phenomenon occurs in one second. The number of times a heart beats in one minute is divided by 60 seconds to obtain the frequency in Hertz.