In this thesis the surgical options for treatment of functional mitral regurgitation (MR) are described. In functional MR, the mitral valve has a normal anatomy, which distinguishes this type of insufficiency from organic MR. Regurgitation in functional MR is related to an abnormal geometry of the left ventricle, which can be the result of an infarction or ischaemia, or may be caused by another—intrinsic—disease of the myocardium. Based on aetiology, we can distinguish ischaemic and non-ischaemic functional MR. Patients with functional MR often present with signs and symptoms of heart failure. Current guidelines do not offer clear treatment algorithms for these patients, and an intervention on the mitral valve is often discouraged, mainly because of contradictory results from studies on surgical interventions on the valve. In this thesis, the role of surgery in the multidisciplinary treatment of patients with functional MR, typically associated with heart failure, is evaluated with regard to clinical and echocardiographic outcomes. The ultimate goal is to establish an individualised medico-surgical approach to this pathology. As such, this thesis results from close collaboration between the departments of Cardiothoracic Surgery and Cardiology of the Leiden University Medical Center. ; Promotores: R.J.M. Klautz, J.J. Bax ; With Summary in Dutch