Systole

This is the name given to the contraction of the heart. It is sometimes separated into an atrial systole and a ventricular systole since contraction of the atrial comes shortly before that of the ventricles. It is followed by relaxation of the heart called diastole. Just before systole the atrioventricular valves (mitral, tricuspid) close, allowing rapid increase in ventricular pressures. Just before diastole, the valves open allowing blood to pass into the ventricles thereby causing a rapid reduction in ventricular pressures but a sustained rise in ventricular volume because of the phenomenon called rapid filling of the ventricles. The above are the events in the cardiac cycle.