Semi-automatic external defibrillator with voice prompts to guide the operator, and automatic evaluation of impedance and ECG signal to assess appropriateness of the shock. Simple and immediate to use, it makes emergency interventions safe and effective, even at the hands of non-medical personnel. The availability of paediatric and adult modes and impedance compensation at the time of discharge ensures precise adjustment of the patient's therapy. It also makes it possible to record the parameters of the event and ECG traces and view them on one’s personal computer.