The period in the cardiac cycle when the left ventricle has the largest volume is the end of atrial systole, when the left ventricle contains the most blood, and the next step is to eject the blood into the aorta through contraction to complete the physical circulation. In the cardiac cycle, the contraction of the atrium is the last step, at first the ventricle through active diastole to form a drop in intraventricular pressure, the blood in the atrium has a pumping effect, at this time the mitral valve opens the blood in the atrium will flow into the left ventricle, but with the increase in blood flow to the left ventricle, the intraventricular pressure gradually increases, the atrium will flow into the intraventricular blood will gradually slow down. At this time, the left atrium enhances intra-atrial pressure by active contraction, which further increases blood flow into the left ventricle to fill it. Toward the end of atrial contraction, the mitral valve closes, and the ventricles contract to increase intraventricular pressure. When the pressure reaches a certain level, the aortic valve opens and the blood enters the aorta, and then from the aorta into the systemic circulation, after some exchange of substances in the capillaries, through the venous recycling into the atrium, the blood is exchanged through the pulmonary circulation, and then re-atrial into the ventricle, completing a whole cycle of circulation.