Different factors cause sudden (acute) and long-standing (chronic) aortic valve regurgitation.
Chronic aortic valve regurgitation
Causes of chronic aortic valve regurgitation include:
Congenital heart defects. Some people are born with a valve that has one (unicuspid valve) or two leaflets (bicuspid valve) instead of three. In either of these cases, the valves don't close the way they should when the heart is at rest.
Aging. The normal wear and tear of aging can affect the valves.
Endocarditis. This is an infection in the heart. Bacteria caused by infection can prevent the valve from closing properly.