Functional, or secondary, mitral regurgitation (MR) develops aspart of the process of remodelling which in turn occurs as a resultof left ventricular failure. Although this complication can resultwhatever the primary pathology causing the left ventricular failure,the pathophysiological process varies to a certain extent dependingon the aetiology. There is some confusion in the literature withrespect to ischaemic MR, with some authors calling all ischaemic MR functional. For the sake of clarity, this chapter deals with functionalMR resulting from left ventricular failure which for the sake of argument I will define as a left ventricular ejection fraction(LVEF) of less than 35%. Functional MR is a common consequence of left ventricularsystolic dysfunction (LVSD) and it has an important bearing onboth symptoms and outcome in patients suffering from heart failure(HF). In a study of 2057 patients with symptomatic HF andwith a LVEF of less than 40% but without structural valve disease,56.2% had some degree of MR and in 29.8% of these it was moderate or severe. Furthermore, the presence of moderate or severeMR was associated with a significantly higher mortality at 1, 3, and5 years. In a multivariate analysis, MR of any degree wasan independent predictor of death. The success of mitral valve surgery, and in particular the flourishingof mitral valve repair techniques, along with the ever-increasingburden of patients with HF, has led to the adaptationof repair techniques, originally developed to correct structuralabnormalities of the mitral valve, to attempt to halt or even reversethe remodelling process.