The Cardiac Cycle Explained: Understanding the Four Phases

Following atrial systole, ventricular systole occurs when both ventricles contract forcefully.This phase has two distinct periods. First is isovolumetric contraction, where ventricular pressure rises rapidly, causing the AV valves to close.Once ventricular pressure exceeds arterial pressure, the semilunar valves open, initiating ventricular ejection. Blood is propelled from the right ventricle into the pulmonary artery and from the left ventricle into the aorta.Ventricular systole lasts about zero point three seconds and is marked by the 'second heart sound' or 'dub' when the semilunar valves close at the end of this phase.