a defibrillator for atrium and / or ventricle having at least two capacitors which in the production of defibrillation pulses are discharged in at least two phases in succession in different configurations , wherein there are provided switching means which control the discharge in the at least two discharge phases in such a way that the mean value of their voltages is substantially equal and no voltages below the rheobase occur in any of the discharge phases , and a corresponding defibrillation method .