A pulse generator housing for enclosing and containing pulse generator defibrillation circuitry. The housing is formed entirely of electrically conductive metal defining an electrically conductive outer surface which is connected to the pulse generator circuitry for delivering defibrillating energy to the heart. The pulse generator housing is implanted in the pectoral region proximate the heart with the conductive surface facing the heart. Regions of the conductive outer surface may be electrically isolated and dedicated for separately sensing and shocking. The outer surface may be coated with platinum. Additional coiled segment electrodes may extend from the housing and be electrically connected to the conductive outer surface so as to increase the effective conductive surface area. A sensor is provided to determine whether the housing is inside or outside a body of a patient to disconnect the pulse generator housing conductive surface from the pulse generator circuitry when the unit is outside the body of a patient.