A medical system (300) is disclosed for treating a defective mitral valve (MV) having an annulus (A). The system (300) comprises in combination a removable and flexible elongate displacement unit (301) for temporary insertion into a coronary sinus (CS) adjacent the valve wherein the displacement unit has a delivery state for delivery into said CS and an activated state to which the displacement unit is temporarily and reversibly transferable from the delivery state. The displacement unit comprises a proximal reversibly expandable portion (302) a distal anchoring portion (303) being movable in relation to the proximal expandable portion in a longitudinal direction of the displacement unit to the activated state in which the shape of the annulus is modified to a modified shape (A ) and an annuloplasty device (102) for permanent fixation at the mitral valve annulus by annuloplasty of the valve when the modified shape is obtained. The annuloplasty device (102) comprises a fixation structure that is adapted to retain the modified shape.
