Functional Mitral regurgitation is a now well known entity due to tethering of the valve either mono-lateral, as happens in lateral myocardial infarction, or bilateral as happens in dilated cardiomyopathy. Treatment of this pathology, either conserving the valve and addressing regurgitation by mean of restrictive annuloplasty, or implanting a prosthesis remains controversial in terms of mid and long term benefit for the patient. The investigators propose a randomized controlled study to compare the efficacy of both technique in terms of mortality and freedom from reintervention.