Left ventricular function was measured by echocardiography in 22 patients with pure mitral stenosis. Thirteen patients underwent closed transventricular mitral valvulotomy and nine underwent open mitral valvulotomy using cardiopulmonary bypass. Preoperative left ventricular function was normal in most patients but was depressed in older subjects (P less than 0.05) and in those undergoing a second operation on the mitral valve (P less than 0.001). The decrease in left ventricular function was probably related to the duration of mitral valve disease, with fibrosis and rigidity of the subvalvar apparatus and posterobasal left ventricular wall. There was no change in ventricular dimensions or in left ventricular function as measured by percentage shortening of the left ventricular diameter and ejection fraction 7 to 12 days after open or closed mitral valvulotomy.