A battery-powered external device designed for the application of rhythmic compression to the chest in the region of the heart to provide blood flow during treatment of cardiac arrest [cardiopulmonary resuscitation (CPR)]. It may be available in a variety of forms but includes a mechanical chest compressor (e.g., plunger-type), a battery-powered control unit, and patient straps/supports. The device is typically used as an adjunct to or substitute for manual external cardiac compression in cases where manual compression is not ideal, or to prevent fatigue and improve consistency (i.e., of force, rate).