Different factors cause sudden (acute) and long-standing (chronic) aortic valve regurgitation to develop.

Chronic aortic valve regurgitation

Causes of chronic aortic valve regurgitation include:

• Congenital heart defects. Some people are born with aortic valves that have only one (unicuspid valve) or two (bicuspid valve) leaflets, instead of the normal valve with three leaflets (tricuspid valve). The structure of these abnormal valves often prevents them from closing completely when the heart is at rest, allowing blood to leak back into the left ventricle. These types of valves are also more susceptible to deposits forming on the surface, which can further impair the valve's ability to close properly.
• Aging. The aortic valve deteriorates with the normal wear and tear on the valve that comes with age.
• Rheumatic fever. Rheumatic fever used to be the most common cause of valvular problems in the United States, but the widespread use of antibiotics has nearly eliminated it in recent years. Rheumatic fever can develop from an untreated strep throat infection. Although individuals generally have rheumatic fever as children, the effects often are not evident until adulthood. It can lead to chronic scarring of the leaflets of the valves and prevent them from closing completely, causing regurgitation.
• Infection in the heart (infective endocarditis). Endocarditis is a common cause of aortic valve regurgitation. When bacteria begin growing on the valve or inside the heart, they form a colony, known as a vegetation, which may grow to be several centimeters in size. These colonies can prevent the valve from closing completely, causing regurgitation. The bacteria also can eat through the valve leaflet, leaving a hole through which blood can leak backward.
• Enlarged aorta (dilation of the aortic root). The portion of the aorta that is connected to the heart is called the aortic root. If it becomes enlarged (aortic root dilation), it can lead to regurgitation by pulling the leaflets of the valve apart and out of shape, causing them to leak. Aortic root dilation can be caused by age, high blood pressure, a disorder of the body's connective tissues (Marfan's syndrome), syphilis, and autoimmune diseases, in which your immune system begins to attack your own body's cells.
• The diet medication fen-phen. Fen-phen was a popular diet drug that was taken off the U.S. market in 1997 because of its link to heart valve disease, including aortic valve regurgitation.
• Radiation treatments for cancer. On rare occasions, radiation treatments to the chest, especially in young people, can damage the aortic valve.

Acute aortic valve regurgitation

Acute regurgitation can be caused by:

• Endocarditis, an infection in the heart. Endocarditis is the most common cause of acute regurgitation.
• Problems with the replacement (prosthetic) aortic valve. Some people who have had surgery to replace the aortic valve develop aortic valve regurgitation with the new valve.
• Aortic dissection. In aortic dissection, blood can leak into a tear in the inner lining of the aorta, causing the walls of the aorta to separate. When a separation occurs, blood can seep into the middle layer of the aorta and damage the vessel and the structure of the aortic valve.
• Trauma to the chest. An injury, such as hitting the dashboard with your chest in a car accident, can damage the valve.

Acute aortic valve regurgitation is an emergency that must be treated immediately with surgery.