Four years' experience with 363 patients, in whom 360 mitral and 65 tricuspid prosthetic valves have been implanted with single continuous sutures, is presented. The occurrence of prosthetic valve detachment is particularly discussed. There were 4 cases of detachment of the prosthetic mitral valve and no cases of tricupsid dehiscence. All 4 patients with detached valves required reoperation. Calcifications that penetrate into the annulus and myxomatous degeneration of the valve are considered more important factors in the production of prosthetic cases so long as a uniform distribution of stitches is maintained (not too close to each other) and excessive tension in the suture line is avoided.