The authors believe that "open mitral commissurotomy is the treatment of choice for the relief of postrheumatic mitral stenosis wherever adequate facilities and personnel are available." This opinion is based on experiences with 200 consecutive open heart operations of this type. A left thoracotomy approach is considered the most important single factor in success with this method. Direct exposure of the valve makes it possible to incise the commissural and subvalvular fusion accurately, to extract intra-atrial clots, to remove loose calcific deposits from the valve cusps, and to correct any associated valvular insufficiency. Of the 200 operations reported, 39 were reoperations and 161 were primary operations. In the last 100 primary operations there were only 2 hospital deaths.