Schwarzenegger was born with a bicuspid aortic valve, an aortic valve with only two leaflets (a normal aortic valve has three leaflets). Schwarzenegger opted in 1997 for a replacement heart valve made of his own transplanted tissue; medical experts predicted he would require heart valve replacement surgery in the following two to eight years as his valve would progressively degrade. Schwarzenegger apparently opted against a mechanical valve, the only permanent solution available at the time of his surgery, because it would have sharply limited his physical activity and capacity to exercise.

What word describes an aortic valve with two rather than three leaflets?