The action of the human heart consists of a series of events, which follow one another with great rapidity.
Main events in cardiac cycle are:
(i) Auricular systole,
(ii) Ventricular systole and
(iii) Joint diastole.
Thus, we can say that the contraction of the heart and its relaxation constitute cardiac cycle or heart beat. The duration of the cardiac cycle varies inversely with the cardiac rate. The heartbeat is 72 times per minute in man. Single heartbeat lasts for 0.8 of a second. In such heart beats, blood comes to heart and then is propelled from auricles to ventricles and then to arteries. The number of heartbeats per minute is very much influenced by age, size, sex, temperature.
