Abstract: External cardiac defibrillators that include automatic or semi-automatic self-contained defibrillators to be used by non-health professionals (physicians, nurses and other specifically trained persons). A power subassembly in an automatic or semi-automatic cardiac defibrillator system which, associated with a computer device, is capable of diagnosing a patient's condition by performing a simplified electrocardiogram, transmitting the data to the electronic device and supplying, controlled by this device, electric shocks to the patient, and also providing or contributing to further ancillary defibrillation functions.