Causes

Causes of mitral valve stenosis include:

• Rheumatic fever. A complication of strep throat, rheumatic fever can damage the mitral valve. Rheumatic fever is the most common cause of mitral valve stenosis. It can damage the mitral valve by causing the flaps to thicken or fuse. Signs and symptoms of mitral valve stenosis might not show up for years.
• Calcium deposits. As you age, calcium deposits can build up around the mitral valve (annulus), which can occasionally cause mitral valve stenosis.
• Radiation therapy. Treatment for certain types of cancer that requires radiation to your chest area can sometimes cause the mitral valve to thicken and harden.
• Other causes. In rare cases, babies are born with a narrowed mitral valve (congenital defect) that causes problems over time. Some autoimmune diseases, such as lupus, also may rarely cause mitral valve stenosis.

How the heart works

The heart, the center of your circulatory system, consists of four chambers. The two upper chambers (atria) receive blood. The two lower chambers (ventricles) pump blood.

Four heart 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 — comprises two flaps of tissue called leaflets.

The mitral valve opens when blood flows from the left atrium to the left ventricle. Then the flaps close to prevent the blood that has just passed into the left ventricle from flowing backward. A defective heart valve fails to either open or close fully.