Mitral valve repair is an attractive procedure for both patients and surgeons because there are many target diseases, its effectiveness and significance are clearer than those of valve replacement, and experience and skill are required. However, the risk of re-operation remains an issue. Re-operation is generally performed 1-3 years after surgery, which is relatively early, with the early re-operation rate being 5-8%. The condition stabilizes thereafter, and re-operation-free rate in the subsequent 10 years is 80-95%. The pathology likely to lead to re-operation includes active infective endocarditis and extensive prolapse of the anterior leaﬂet, and the cause includes incomplete repair, injury of the sutured segment, re-dilatation of the annulus, re-elongation of the shortened chorda tendineae, and hemolysis. To achieve a favorable outcome, identification of the mechanism of mitral regurgitation by means of echocardiography and selection of an appropriate repair procedure for it are necessary. For the repair procedure, resection and suture are the basic procedure, and it is necessary to achieve complete leaﬂet coaptation at completion of repair, and to implant the annuloplasty ring carefully. Prevention of dehiscence in resection and suture is especially important. Intraoperative transesophageal echocardiography should only be performed by an experienced sonographer, and residual regurgitation of 2 cm2 or more should be re-investigated and treated. Re-regurgitation during the hospital stay should be treated, and re-operation should be performed if necessary, which results in a favorable late outcome. In this feature article, we describe information required by surgeons before surgery, in addition to the issues described above.