The heart, the center of your circulatory system, consists of 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 to let blood flow in only one direction through your heart. The mitral valve — which lies between the two chambers on the left side of your heart — consists of two triangular flaps of tissue called leaflets.

Heart valves open like a trapdoor. The mitral valve is forced open when blood flows from the left atrium into the left ventricle. When the blood has gone through the valve, the leaflets swing closed to prevent the blood that has just passed into the left ventricle from flowing backward, in the wrong direction.

A defective heart valve is one that fails to either open or close fully. When a valve becomes narrowed and blood flow through it is limited, the condition is called stenosis. Mitral valve stenosis is narrowing of the mitral valve, which obstructs blood flow into the heart's left ventricle.

Causes of mitral valve stenosis include:

  • Rheumatic fever. A complication of strep throat, rheumatic fever can damage the mitral valve, leading to mitral valve stenosis later in life. Rheumatic fever is the most common cause of mitral valve stenosis. It 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. Or the infection may cause the leaflets of the mitral valve to fuse somewhat together, preventing the valve from opening and closing properly. People with rheumatic fever may have both mitral valve stenosis and regurgitation.
  • Congenital heart defect. In rare cases, babies are born with a narrowed mitral valve and develop mitral valve stenosis early in life. Babies born with this problem usually require heart surgery to fix the valve. Others are born with a damaged mitral valve that puts them at risk of developing mitral valve stenosis when they're older. In most cases, doctors don't know why a heart valve fails to develop properly in a newborn, infant or child, so it's not something that can be prevented.
  • Other causes. Rarely, growths, blood clots or tumors can block the mitral valve, mimicking mitral valve stenosis. As you age, excessive calcium deposits can build up around the mitral valve, which sometimes causes significant mitral valve stenosis. Radiation treatment to the chest and some medications also may cause mitral valve stenosis.
Sep. 15, 2011

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