Aortic stenosis: Narrowing (stenosis) of the heart valve between the left ventricle of the heart and the aorta. This narrowing impedes the delivery of blood through the aorta to the body and makes it tough for the heart to carry out this Herculean task. A normal aortic valve has three leaflets or cusps, but a stenotic valve may have only one cusp (unicuspid) or two cusps (bicuspid), which are thick. stiff and stenotic. Some children with aortic stenosis have chest pain, unusual fatigue, dizziness or fainting. Many children have few or no symptoms. The need for surgery depends on the degree of stenosis. Although surgery may enlarge the stenotic valve the valve remains deformed and eventually may need to be replaced with an artificial one. A procedure called balloon valvuloplasty has been used in some children with aortic stenosis. Persons with aortic stenosis need medical follow-up all their lives since even mild stenosis may worsen over time and need treatment.