Mitral stenosis is almost invariably acquired and is practically always the result of rheumatic fever. It is most frequently found between the ages of 15 and 40 and is more common in females than males by a ratio of three to two. Mitral insufficiency may be either organic or relative. Relative mitral insufficiency is secondary to dilatation of the left ventricle, which may occur from a number of causes. Organic mitral insufficiency is also almost always the direct result of rheumatic fever. The former is of more serious import as it usually occurs in a dilated heart. Organic mitral insufficiency may exist for years without impairing the efficiency of the heart but often is followed by mitral stenosis or subacute bacterial endocarditis. Although mitral insufficiency may persist alone for many years, very commonly the signs of insufficiency disappear, stenosis develops or the patient may succumb to subacute bacterial endocarditis, an