A device, a kit and a method is presented for permanently augmenting the pump function of the left heart. The mitral valve plane is assisted in a movement along the left ventricular long axis during each heart cycle. The very close relationship between the coronary sinus and the mitral valve is used by various embodiments of a medical device providing this assisted movement. By means of catheter technique an implant is inserted into the coronary sinus, the device is augmenting the up and down movement of the mitral valve and thereby increasing the left ventricular diastolic filling when moving upwards and the piston effect of the closed mitral valve when moving downwards.