Normal aortic valve. A normal aortic valve opens fully to let blood flow into the aorta. The aortic valve has three flaps that work like a one-way gate. When the heart pumps, the aortic valve opens to allow oxygen-rich blood to flow from the left ventricle into the aorta. When the heart rests between beats, the aortic valve closes to keep blood from flowing backward into the heart.

Aortic valve stenosis. With aortic valve stenosis, the valve cannot open as wide as normal. Because the valve does not open as wide, the heart must work harder to pump blood through the valve.