A medical device such as an external defibrillator delivers electrical therapy using a special ascending, biphasic waveform. The special waveform is characterized by a set of at least two peaks. The amplitude of the second peak is greater than the amplitude of the first peak. The waveform is generated by switching capacitance configuration in the defibrillator from a parallel configuration to a series configuration while the defibrillator is delivering the defibrillation shock to the patient. Because of the switching capacitances and/or the waveform, the external defibrillator can be made physically smaller and weigh less, without sacrificing the therapeutic effect of a larger external defibrillator that would deliver a defibrillation shock of higher energy. As such, the defibrillator is easier to configure for transporting, handling, and even wearing.