Most people who have aortic valve stenosis are born with a normal, healthy aortic valve but develop aortic stenosis late in life. Aging and calcium buildup cause the leaflets of the valve to thicken and harden, preventing the valve from opening properly. Typically, stenosis develops slowly over many years.

Aortic valve stenosis also occurs in people who are born with a valve that has two flaps instead of three (congenital bicuspid valve) or in people who have had rheumatic fever. In either of these cases, the leaflets do not open as widely as they should. This creates a smaller opening and makes it much harder for blood to flow from the left ventricle into the aorta.