Abstract: A defibrillator (10) is disclosed in which measured information concerning the energy delivered by the defibrillator to a meter (56) is employed to calibrate subsequent discharges by the defibrillator at the same energy level. In connection with that process, a microprocessor (70) controls the operation of a feedback loop (50), including a controlled-gain amplifier (64), level detector (66), adder (68) and energy charger (58), to adjust the voltage applied to a discharge capacitor (54) in response to the energy measured by the meter. The information can be input to the microprocessor either manually or automatically and can be used by the microprocessor in performing a piecewise linear approximation of the voltage adjustment required to deliver the desired nominal energy, or in performing a direct computation of that adjustment. This process is repeated for each of the energy levels selectively dischargeable by the defibrillator.