A 58-year-old woman, who had congestive heart failure due to mitral regurgitation after percutaneous transvenous mitral commissurotomy, underwent mitral valve replacement. It is reported that mitral regurgitation more often occurs after PTMC in patients with severely calcified mitral valve or advanced subvalvular lesion than in those without. Our experience indicated that PTMC should be carefully performed in institutions which have a surgical team ready for emergency operation.