Mitral regurgitation (MR) may be classified into two major categories: primary and secondary (functional). In primary MR, disease of the valve itself (eg, myxomatous degeneration, rheumatic disease) causes valve incompetence, producing left ventricular (LV) volume overload. To compensate, the left ventricle must enlarge in order to increase its volume-pumping capacity. If volume overload is prolonged and severe, the adverse effects of remodeling together with activation of deleterious neurohumoral systems leads to myocardial damage. It is quite clear that correction of the volume overload causes myocardial healing and reverse remodeling. Conversely, in secondary MR, the valve itself is normal. Ventricular dilatation and wall motion abnormalities cause papillary muscle displacement and annular dilatation, causing a normal mitral valve to leak. In this situation it is not clear whether or when correction of the MR is beneficial because the MR was not the primary cause of the LV dysfunction to begin with. Other areas of uncertainty include the type of correction to be used and whether burgeoning technologies for percutaneous valve repair will be useful.