The cardiac cycle consists of one heart beat or one cycle of contraction and relaxation of the cardiac muscle. The contraction is called the systole while the relaxation phase is called the diastole. The successive phase of cardiac cycle are-
(i) Atrial systole - contraction of auricles
(ii) Ventricular systole - contraction of ventricles
(iii) Complete cardiac diastole or joint diastole - relaxation of both auricles and ventricles.