The aortic valve is located between the aorta and the heart's left ventricle. The pulmonary vein delivers oxygenated blood to the heart's left atrium. Then it passes through the mitral valve and into the left ventricle. With each of the heart muscle’s contractions, oxygenated blood exits the left ventricle through the aortic valve. In most cases, three flaps comprise the valve. Due to a congenital (present at birth) condition, some valves may feature only two flaps. As a part of the cardiac system, the valve is susceptible to two major conditions: aortic stenosis and aortic regurgitation. Aortic stenosis occurs if the valve fails to open all the way. This disease affects the blood's ability to effectively move into the aorta, and blockage may occur. This condition may be caused by rheumatic fever or degenerative calcification. Congenital conditions have also been known to cause aortic stenosis. Aortic regurgitation occurs if oxygenated blood flows in the wrong direction. This happens when the aortic valve is not functioning correctly. Essentially, blood is pumped into the aorta, but the valve does not keep it from reentering the left ventricle.