A pulse generator having a housing for enclosing and containing pulse generator defibrillation circuitry, particularly adapted to allow for ease of manufacture and use, is disclosed. At least one surface of the housing is electrically conductive and connected to the pulse generator circuitry for delivering defibrillating energy to the heart. The defibrillator is provided with a case activating lead connector cavity having two connector blocks. By plugging in a lead with a pin long enough to contact the only first connector block, the lead becomes active. Using a plug with a longer pin to contact both blocks activates the can. To use neither a lead in the case activating port, nor an active can, a plug with a short or nonconductive pin may be used 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 pulse 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 pulse generator housing electrode.