A medical system (100) for treating a defective mitral valve having an annulus, where the medical system comprises in combination； a removable elongate displacement unit (101) for temporary insertion into a coronary sinus (CS) adjacent the mitral valve, wherein the displacement unit has a delivery state for delivery into the CS and in which state the displacement unit is bendable in an arch shape at a portion thereof upon the delivery, and an activated state to which the displacement unit is temporarily and reversibly transferable from the delivery state, whereby at least a portion of the displacement unit is temporarily movable in a radial direction of the CS towards the valve in such a manner that the shape of the annulus is modified to a modified shape. The medical system further comprising an annuloplasty device (102) for permanent fixation at the mitral valve annulus by annuloplasty of the valve when the modified shape is obtained, wherein the annuloplasty device comprises a fixation structure that is adapted to retain the modified shape.
