There are two types of aortic valve problems: stenosis and insufficiency.
The aortic valve has three leaflets, which open and close to prevent blood from leaking back into the heart.
Valve stenosis is when the inside of the valve gets smaller. When this happens, the heart has to push harder to get blood through the smaller opening. This makes it very hard for the blood to circulate through the heart and to the rest of the body. Stenosis may be caused by a build-up of calcium on the valve. This build-up also hardens the valve, which means it can't open and close properly.
Insufficiency or leakage is another problem that can occur when a valve does not close properly. This allows blood to leak back through the valve, away from the direction it should be going. Insufficiency can be caused by a valve that has simply become weak over time and is beginning to wear out. In younger patients, aortic valve disease can be caused by having a bicuspid valve - which has only two leaflets, instead of three. Over time, the bicuspid valve can weaken and may leak or become narrow.
A less common cause of valve disease is an infection called rheumatic fever. This infection may have damaged the valve and caused scarring. The scarring makes it harder for the valve to work properly.