A defibrillator having a housing for enclosing and containing defibrillation pulse generator circuitry, particularly adapted to allow for ease of manufacture and use. At least one surface of the housing is electrically conductive and connected to the defibrillation pulse generator circuitry for delivering defibrillating energy to the heart. The defibrillator is provided with a case-activating lead connector cavity having two isolated conductive elements. By tightening a first setscrew onto a lead connector pin, an electrode of the lead becomes active. Tightening a second setscrew activates the can. Tightening both setscrews onto a plug pin activates the can alone. To use neither a lead in the case-activating port, nor an active can, only one setscrew may be tightened onto a conductive or nonconductive pin to plug the cavity without activating the can. By using this system, various electrode configurations can be used as required to provide the optimum system for a given patient. The defibrillator generator housing is preferably implanted in the left pectoral region proximate the heart with the conductive surface facing the heart. Other implantable electrodes are discharged against the defibrillator generator housing electrode.