The aortic valve, between the left ventricle and the aorta, is narrowed. This makes it hard for the heart to pump blood to the body. Aortic stenosis occurs when the aortic valve didn't form properly. A normal valve has three leaflets or cusps, but a stenotic valve may have only one cusp (unicuspid) or two cusps (bicuspid), which are thick and stiff. (See bicuspid aortic valve below.)

Sometimes stenosis is severe and symptoms may occur in newborns or in infancy. Otherwise, most children with aortic stenosis have no symptoms. In some children, chest pain, unusual tiring, dizziness or fainting may occur. The need for surgery depends on how bad the stenosis is. In children, a surgeon may be able to enlarge the valve opening. Although surgery may improve the stenosis, the valve remains deformed. Eventually, the valve will usually need to be replaced with an artificial one.

A procedure called balloon valvuloplasty has been successful in some infants and children with aortic stenosis. The long-term results of this procedure are still being studied. Children with aortic stenosis need lifelong medical follow-up. Even mild stenosis may worsen over time, and surgical relief of a blockage is sometimes incomplete. Check with your paediatric cardiologist about limiting some kinds of exercise.

People with aortic stenosis, before and after treatment, are at risk for getting an infection of the valve (endocarditis). To help prevent this, they'll need to take antibiotics before certain dental and surgical procedures.