Aortic Valve

The aortic valve is one of the four valves of the heart. It normally has three leaflets, although 2% of the population are born with aortic valves that have only two leaflets. It lies between the left ventricle and the aorta. 

During ventricular systole, pressure rises in the left ventricle. When the pressure in the left ventricle rises above the pressure in the aorta the aortic valve opens, allowing blood to exit the left ventricle into the aorta. 

When ventricular systole ends, pressure in the left ventricle rapidly drops and the high aortic pressure forces the aortic valve to close. The closure of the aortic valve contributes to the second heart sound (S2, "dup").