THE VALUE of mitral valvotomy as a treatment of symptomatic mitral stenosis is an established fact.1-6The effect of valvotomy on the natural history of mitral stenosis and an evaluation of the factors influencing survival after surgery will be the subject of this discussion. Material and Methods A prospective study of patients with predominant mitral stenosis undergoing mitral valve surgery was initiated by Drs. Borden, Baronofsky, and Richards7at the University of Minnesota Hospitals in 1950. This report is a follow up study of the initial 100 consecutive cases of mitral stenosis operated on between June 1950 and September 1953. Two patients originally treated have been lost to follow up. Table 1 indicates the preoperative clinical status of the patients according to the New York Heart Association classification. Patients were selected for surgery primarily for the relief of symptoms secondary to pulmonary hypertension. However, 20 patients were operated