Your heart, which is the pump of your circulatory system, has four chambers. The two upper chambers, the atria, receive blood. The two lower chambers, the ventricles, pump blood.

Blood flows through your heart's chambers, aided by four heart valves. These valves open and close, allowing blood to flow through your heart in only one direction. The mitral valve — which lies between the two left chambers of your heart — has two triangular-shaped flaps of tissue called leaflets.

Heart valves open like a trapdoor. The leaflets of the mitral valve open when the left atrium contracts, forcing blood through the leaflets and into the left ventricle. When the left atrium relaxes between heart contractions, the flaps shut to prevent blood that has just passed into the left ventricle from flowing backward, in the wrong direction.

When working properly, heart valves open and close fully. In mitral valve regurgitation, the mitral valve doesn't close tightly. So, with each heartbeat, some blood from the left ventricle flows backward into the left atrium, instead of forward into the aorta. Regurgitation refers to this backflow of blood through the heart valve.

Causes of mitral valve regurgitation

Mitral valve regurgitation can be caused by many things, including:

  • Mitral valve prolapse. Mitral valve prolapse is a condition in which the leaflets and tendon-like cords supporting the mitral valve weaken. The result is that with each contraction of the left ventricle, the valve leaflets bulge (prolapse) up into the left atrium. This common heart defect may prevent the mitral valve from closing tightly and lead to regurgitation. However, mitral valve prolapse is common and most people who have it never develop severe regurgitation.
  • Damaged tissue cords. Mitral valve regurgitation may result from damage to the tissue cords that anchor the flaps of the mitral valve to the heart wall. Over time, these cords may stretch or suddenly tear, especially in people with mitral valve prolapse. A tear of these cords can cause substantial leakage through the mitral valve and may require repair by heart surgery.
  • Rheumatic fever. Rheumatic fever — a complication of untreated strep throat and once a common childhood illness in the United States — can damage the mitral valve, leading to mitral valve regurgitation later in life. Rheumatic fever can damage the mitral valve in two main ways. The infection may cause the leaflets of the valve to thicken, limiting the valve's ability to open. This causes narrowing of the valve, a condition known as mitral valve stenosis. The infection may also cause scarring of the mitral leaflets, leading to regurgitation. People with rheumatic fever, which is still common in countries where antibiotic use isn't common, may have both mitral valve stenosis and mitral valve regurgitation.
  • Endocarditis. The mitral valve may be damaged by endocarditis, an infection of the lining (endocardium) of the heart that can involve heart valves.
  • Wear and tear on the valve. The mitral valve opens and shuts tens of thousands of times every day of your life. Sometimes age-related wear and tear on the valve causes mitral valve regurgitation.
  • Prior heart attack. A heart attack can damage the area of the heart muscle that supports the mitral valve, affecting the function of the valve. In fact, if the damage is extensive enough, a heart attack may result in sudden and severe mitral valve regurgitation. This sudden onset of regurgitation is sometimes referred to as acute mitral valve regurgitation.
  • Untreated high blood pressure. Over time, high blood pressure can cause your heart to work harder, and gradually your heart's left ventricle can enlarge. This can then stretch the tissue around your mitral valve, which can lead to leakage.
  • Congenital heart defects. Some babies are born with defects in their hearts, including damaged heart valves.

Severe mitral valve regurgitation — regardless of its cause — can weaken your heart. When the left ventricle contracts in a heart with mitral valve regurgitation, some blood flows backward into the left atrium instead of flowing forward into the aorta. As a result, blood flow to the rest of your body decreases. In response, the left ventricle may enlarge (dilate) so that it can pump more blood with each heartbeat. At first this adaptation helps your heart beat with more force. But eventually, the change weakens your heart and may cause heart failure and heart rhythm irregularities, such as atrial fibrillation.

Sep. 15, 2011

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