During the past six years we have operated on 80 patients with predominant mitral insufficiency. Twenty-two patients had ruptured chordae tendineae. Rheumatic heart disease was frequently the cause when there was considerable valve deformity and ruptured chordae to the anterior mitral leaflet. The etiology of these cases was rheumatic heart disease in only 2 of the 15 patients with ruptured chordae to the posterior leaflet. In eight the etiology was unknown. These cases had a syndrome in which there is an aortic as well as an apical systolic murmur. The left atrium was frequently not so large as in rheumatic mitral insufficiency, and most patients were in sinus rhythm. Because of a relative excess of reserve tissue of the posterior leaflet, localized rupture of chordae to this leaflet can easily be corrected by a simple plication procedure.