The surgical treatment of less than severe (≤2+/4+) functional tricuspid regurgitation (TR) in patient undergoing mitral valve surgery, is still controversial: some observational studies have suggested that performing tricuspid annuloplasty in patients undergoing mitral valve surgery with a dilated tricuspid annulus, and TR≤2+ may provide a clinical benefit, while in other observational studies such benefit has not been documented. The ESC Guidelines assign the class IIa recommendation for surgical treatment in patients with tricuspid regurgitation ≤2+ and a dilated annulus, if surgery is concomitant to the repair or replacement of the mitral valve. However the level of evidence C (expert opinion) confirms the absence of clear scientific evidence to support this recommendation. It is therefore very important to carry out randomized trials designed to really prove the supposed efficacy of prophylactic tricuspid annuloplasty, especially in patients with degenerative etiology where the data are particularly controversial. The aim of the study will be to establish the effectiveness of the tricuspid annuloplasty in the early stage of TR. The investigators enrolled patients with TR≤2+ and annular dilation undergoing mitral valve repair. Primary end-point will be the freedom from recurrence of TR≥3+ and from progression of 2 degrees of TR compared to pre-operative, at discharge and 12 months after surgery, assessment by transthoracic echocardiography. Secondary endpoints are to demonstrate the superiority of combined treatment (M \& T Repair Group) compared to single treatment (Mitral-Only Group) at 5 and 10 years after surgery. This will be an experimental superiority, prospective, spontaneous, multicenter, randomized trial. Patients will be randomly assigned to two parallel arms with an allocation ratio 1:1 stratified by center, to receive mitral repair only (Mitral-Only group) or both mitral and tricuspid repair (M \& T Repair group).