It is necessary for patients with implanted medical devices to have surgery in order to change devices whose battery cells have run out. We have suggested changing the battery into a secondary rechargeable one with contactless energy transmission, but it has been difficult to transmit electrical energy without increasing the eddy loss caused by the metal case of the device. We designed a rechargeable cardiac pacemaker with contactless electrical energy transmission and confirmed that it has a secondary power transmission efficiency of 26-40% at 0.4 W. However, an implantable cardioverter defibrillator (ICD) needs a larger volumetric battery than a cardiac pacemaker. It is necessary to transmit a large amount of power without increasing the eddy current loss, and it is important to estimate the eddy loss caused by the metal case.