The heart has four chambers, two small ones above (atria) and two large ones below (ventricles). Each chamber has a one-way inflow valve and a one-way outflow valve. The tricuspid valve opens from the atria to the ventricles, while the pulmonary valve opens from the ventricles to the pulmonary arteries. Opening from the left atrium into the left ventricle is the mitral valve, while the aortic valve opens from the left ventricle to the aorta. The various valves of the heart can become dysfunctional due to valve leakage (valve regurgitation) or incomplete valve opening (valve stenosis). Each of these problems will severely interfere with the heart’s ability to pump blood. Sometimes both lesions can be present in the same valve. Mitral valve insufficiency means that some blood flows back from the left ventricle into the left atrium with each ventricular contraction. When the left ventricle contracts and pumps (blood flows from the left ventricle into the aorta), some of the blood flows back into the left atrium, thereby increasing the volume and pressure in the left atrium; this subsequently increases the pressure in the vessels from the lungs to the heart in turn, resulting in fluid retention (stasis) in the lungs. Mitral valve prolapse, in which the mitral valve leaflet projects toward the atrium during ventricular contraction and can sometimes return a small amount of blood to the left atrium, is a common cause of mitral regurgitation. In North America and Europe, a more common cause of mitral regurgitation is myocardial infarction, which results from an episode of myocardial infarction that damages the supporting structures of the mitral valve. Another common cause is mucinous neoplasia, when the valve becomes progressively flaccid. 1. Symptoms Mild mitral regurgitation may have no symptoms and can only be diagnosed by a physician with the aid of a stethoscope. Through the stethoscope, the characteristic murmur due to blood regurgitation can be heard. 2. Pathophysiology As the left ventricle has to pump more blood to compensate for the regurgitation, the left ventricle will gradually grow to increase the force of each beat. The growing ventricle can cause palpitations, especially when the patient is lying on the left side. The left atrium also tends to grow in size to accommodate the regurgitant blood from the left ventricle. A significantly enlarged left atrium often has extremely fast and irregular arrhythmias (atrial fibrillation), which further reduces the heart’s pumping function. The left atrium in fibrillation does not contract effectively, making it easy for stagnant blood to form a clot. When this clot breaks up and travels throughout the body with the blood through the heart, it causes infarction of small arteries, which may lead to stroke or other damage. Severe regurgitation is enough to cause heart failure to occur, with coughing, shortness of breath with activity, and lower extremity edema. 3. Diagnosis The characteristic murmur produced by mitral regurgitation makes it easy for the physician to make a diagnosis. Electrocardiograms and chest X-rays may show the presence of left atrial and left ventricular enlargement. The most valuable diagnostic tool is the echocardiogram, which clearly shows the diseased valve and allows evaluation of the severity of the lesion. If regurgitation is severe, valve repair (valvuloplasty) or valve replacement (with mechanical or biological valves, the latter derived from porcine heart valves) is best performed before irreversible damage to the left ventricle occurs. The primary goal of valve repair is to reduce the regurgitant flow of blood so that the patient can tolerate the symptoms that occur and prevent further damage to the heart. Each type of replacement valve has its advantages and disadvantages. Although mechanical valves are usually effective, they are prone to thrombosis and should be accompanied by anticoagulants. Porcine valves work well and are less prone to thrombosis, but the short life span of the valve compared with mechanical valves is the biggest regret. If the replacement valve is destroyed, the valve must be replaced immediately.