This is probably the most common congenital heart defect. The normal aortic valve has three flaps, or cusps, that open and close. A bicuspid valve has only two flaps, rather than three. There may be no symptoms in childhood, but by adulthood (often middle age or older) the valve can become stenotic (narrowed), making it harder for blood to pass through it, or regurgitant (allowing blood to leak backward through it). Treatment depends on how well the valve functions.

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