Ventricular Systole
Ventricular systole is the contraction of the muscles (myocardia) of the left and right ventricles.
At the later part of the ejection phase, although the ventricular pressure falls below the aortic pressure, the aortic valve remains patent because of the inertial energy of the ejected blood.
The graph of aortic pressure throughout the cardiac cycle displays a small dip (the "incisure" or "dicrotic notch") which coincides with the aortic valve closure. The dip in the graph is immediately followed by a brief rise (the "dicrotic wave") then gradual decline. Just as the ventricles enter into diastole, the brief reversal of flow from the aorta back into the left ventricle causes the aortic valves to shut. This results in the slight increase in aortic pressure caused by the elastic recoil of the semilunar valves and aorta.
The total volume of blood remaining in the ventricle just at the end of the ventricular contraction is called end-systolic volume (ESV).
Read more about this topic: Cardiac Cycle