The mitral valve is between the left atrium and left ventricle of the heart; it can become constricted (stenosis), or leak (insuffiency). Mitral stenosis is caused by inflammation of the valve in rheumatic fever; over the years scar tissue forms in the valve, causing constriction. As a result the left atrium has difficulty in pumping blood from the lungs into the left ventricle, so that the lungs become excessively full of blood, resulting in shortness of breath, coughing and cyanosis. Tension on the wall of the right atrium can cause atrial fibrillation. Mitral valve stenosis is treated by medication to stimulate correct heart function; in severe cases the valve can be replaced by an artificial one. Mitral insufficiency can also be caused by rheumatic fever, but often results from old age or damage to part of the valve by coronary infarction. Leakage of blood to the left atrium raises blood pressure in the lungs; the symptoms are thus more or less the same as in mitral stenosis, but often less severe. In most cases the symptoms may be removed by medication (including diuretics). An artificial valve may be substituted for the disordered one.