An energy adjusting circuit for use with a defibrillator. The energy adjusting circuit reduces the defibrillation pulse energy that would otherwise be applied to the patient by the defibrillator. The energy adjusting circuit can be part of the defibrillator itself, or part of an adapter coupled to the output ports of a conventional defibrillator. In an adapter designed for pediatric defibrillation, the adapter may include paddles configured for use on babies and small children. The energy adjusting circuit may be formed entirely from passive components and may include a divider circuit with two resistors. The resistance of the two resistors is selected so as to absorb a predetermined percentage of the defibrillation pulse energy that would otherwise be applied to the patient. An isolation circuit may be further included to assist with the measurement of ECG signals through the electrodes. The components of the energy adjusting circuit can be selected so as to produce a defibrillation waveform that has a desired pulse width and tilt, both of which are approximately fixed over an expected range of patient impedances. The defibrillator may be configured to recognize the presence of the energy adjusting circuit, and to indicate to the user that the energy selection ranges have been adjusted accordingly.