The most common aortic valve problem in young people is to be born with only two leaflets (bicuspid) instead of three (tricuspid), usually resulting in stenosis. This abnormal structure causes turbulence in the blood flow that creates stress points on the valve. Statistically, bicuspid valves are three times more common in men than in women. Symptoms may occur at birth or appear after many years. It is estimated that at least 1% of the population in America is born with a bicuspid aortic valve.

The body responds to the repeated trauma of opening and closing this abnormal valve by trying to strengthen the tissue. This "strengthening" often produces scarring and ultimately calcification, both on and around the valve, which restricts blood flow. If the valve scars partially shut, the heart must produce more pressure to get the same amount of blood across the valve. Thus, the heart must work harder.

Fortunately, the body is engineered with considerable reserve. Most people do not notice symptoms until the opening is less than half the normal size. Symptoms commonly associated with this disorder are shortness of breath during strenuous activity, chest pain, dizziness, or fainting. Greater demands placed on the heart by strenuous activity cause these symptoms, because the heart is already using its reserve capacity.

The severity of stenosis is expressed by pressure gradient and valve area determined by echocardiogram. The velocity of the red blood cells is determined by the echo Doppler method and formulas have been developed to translate this into pressure and area measurements. The normal aortic valve has a valve area of about 2.5 square centimeters. Most patients do not experience any problems until this falls to less than 1.0. By the time it reaches 0.6 most have symptoms of shortness of breath or chest pain on exertion. Fainting can also occur. A valve of 0.3 is considered too small to survive.

In general, guidelines for surgery in aortic stenosis recommend holding out until symptoms develop. However, stress testing may also be appropriate in patients who have extreme exertional demands to see what happens to the heart under controlled conditions. Sudden death in young athletes happens too often when unsuspected aortic stenosis is pushed to extremes.