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Stenosis is a medical term for narrowing. Aortic stenosis refers to narrowing of the valve at the outlet of the main pumping chamber (left ventricle) of the heart. This valve normally opens widely when the heart contracts and blood is ejected from the ventricle, and it closes tightly to prevent blood from flowing back from the aorta between contractions.
Aortic stenosis can create extra work for the heart as it tries to pump a normal amount of blood through a narrowed opening. This may result in enlargement and thickening of the heart muscle and lead to fainting spells, cardiac pain (angina) and congestive heart failure. The underlying cause may be from valve damage due to rheumatic fever or from degeneration and calcification of a valve that was abnormal at birth. The aortic valve normally has three cusps (cup-shaped folds of tissue) that open widely as blood leaves the left ventricle and come together as the valve closes. About 1 percent of people are born with an aortic valve that has only two cusps (congenital bicuspid aortic valve). These valves may leak (aortic insufficiency) or become stenotic later in life.
Surgical removal of a stenotic aortic valve and replacement with a prosthetic valve usually restores heart function to normal. Such valves may be made of animal tissue or from metal and synthetic materials. See the graphic below for two examples of artificial heart valves.