What causes a leaky heart valve?

Not man made.: All biologic valves leak a little. They do not close perfectly.

Born with vs acquire: Leaky heart valves occur congenitally when some aspect of the valve leaflets/annulus/supporting structures is abnormal at birth. They can also be acquired as a result of changes in the heart structure/valve structure/aorta/lungs over time. Heart attacks can damage valves, as can infectious endocarditis, cardiomyopathy, enlarging aortic root, pulmonary disease causing pulmonary hypertension.