The heart delivers oxygen and nutrients to the body by pumping blood. There are two sides to the heart. The chambers on the right side of the heart receive deoxygenated blood and pump it to the lungs, which infuse the blood with oxygen. This oxygen-rich blood then travels to the chambers on the left side of the heart. The blood enters the left heart through the top chamber (the left atrium, a “collecting” chamber) which squeezes it through a valve into the bottom chamber (the left ventricle, a “pumping” chamber). The left ventricle then pumps the blood to the rest of the body. The valve between the left atrium and left ventricle is called the mitral valve. Because the left side of the heart pumps blood to the rest of the body while the right side merely pumps it to the lungs, blood on the left side of the heart is at a higher pressure than blood on the right. Because blood on the left side is at a higher pressure, the mitral valve wears out more frequently than its corresponding valve on the right side of the heart.

There are two types of mitral valve disease. The first, called mitral-valve stenosis, occurs when the valve’s tissues are stiff or the valve opening is narrow. When there is stiffness or narrowness, the left atrium cannot pump as much blood into the left ventricle as it is supposed to. Because less blood gets to the ventricle, each pump of the heart delivers correspondingly less blood to the body. As a result, people with mitral-valve stenosis often suffer the symptoms of heart failure—fatigue when walking or exercising, fluid buildup in the tissues caused by weak circulation, and a bluish pallor that results from blood not getting to the extremities. In addition, the heart may enlarge in order to pump harder. This enlargement can cause atrial fibrillation, a condition in which the top chamber of the heart does not contract normally. Mitral-valve stenosis can be congenital or acquired (often as a complication of rheumatic fever) and is usually treated with surgical repair or replacement of the valve.

Mitral-valve insufficiency (sometimes called mitral-valve incompetence or regurgitation) occurs when the mitral valve does not close completely after the atrium contracts. Because the valve remains partially open, some of the blood pumped by the left ventricle leaks back into the left atrium instead of traveling to the rest of the body through the aorta. Insufficiency causes many of the same symptoms as stenosis: heart-muscle enlargement, heart-failure complications, and sometimes atrial fibrillation. The disorder can be caused by hereditary connective-tissue disorders, rheumatic fever, and heart attack. Treatment usually requires surgical repair or replacement of the valve.

Tissue malformations before birth can cause mitral valve disease. For example, the opening of the mitral valve may not grow wide enough during development, or the two leaflets of the mitral valve, which ordinarily stop the backflow of blood from the left ventricle to the left atrium, are shaped irregularly. Myxomatous degeneration, a connective-tissue disorder that people are born with, can make the valve’s leaflets weak and therefore insufficient. Infection can also alter the valve’s structure. Rheumatic fever, which is a complication of untreated childhood scarlet fever, can cause scarring and calcification in valve tissues. In the United States, mitral-valve disorders induced by untreated rheumatic fever is generally limited to third-world immigrants and the elderly—two groups of people who may not have had access to antibiotics during childhood. In the developing world, where the use of antibiotics is not as routine as in the U.S., rheumatic heart disease is common.

Many of the risk factors for patients who acquire mitral-valve abnormalities are not known. Infections that cause heart-valve abnormalities tend to affect drug abusers or those with compromised immune systems. Coronary artery disease and heart attack can also cause valve malfunction. Those with hereditary connective-tissue disorders such as Marfan’s syndrome may be at increased risk of mitral valve disease.

Often an abnormal heart sound (murmur) heard through a stethoscope is the first step in diagnosis. After a physical exam, the doctor will often perform an echocardiogram. This is a non-invasive test that creates an image of the heart with painless ultrasound waves sent from the chest surface. If a sharper image is necessary, a more invasive echocardiogram, in which an ultrasound scope is inserted down the esophagus, may be performed. Most patients over the age of 50 with mitral valve disease will require a coronary angiogram to define the anatomy of the coronary arteries before surgery is performed on the mitral valve. If patients are found to have coronary-artery blockages, then coronary-artery bypass surgery can be performed at the same time as valve repair or replacement.

The most common complication of mitral valve disease is congestive heart failure. Another is embolism, which occurs when a particle in the circulation blocks a blood vessel. When a diseased mitral valve develops an infection (endocarditis), a part of the infected valve can break off. This piece of mitral valve can then travel through the bloodstream. If it blocks a blood vessel and causes an embolism, the patient may suffer a stroke or loose circulation in a limb.

Diet and exercise can help prevent coronary artery disease, which is one cause of mitral valve malfunction. Those with connective-tissue disorders, palpitations, or heart failure should be evaluated regularly to check for valve function.