Pressure of the blood in the ventricles rises when the ventricle myocardium contracts. During most of the cardiac cycle (systole+diastole), the ventricular pressure is less than the pressure in the aorta. During the systole (contraction), the ventricular pressure rapidly increases. When the pressure of ventricle becomes equal to the pressure of the aorta, the aortic valve opens, and blood is pumped to the body.
