Methods and systems are provided that comprise: sensing cardiac events of a heart； utilizing one or more processors to perform: declaring a ventricular fibrillation (VF) episode based on the cardiac events charging a single charge storage capacitor； delivering a multi-phase VF therapy that includes phase I and phase II therapies, wherein: a) during the phase I therapy, a combination of two or more medium voltage (MV) shocks are delivered entirely from the single charge storage capacitor； and b) during the phase II therapy, a low voltage pulse train is delivered at least partially from the single charge storage capacitor. Methods and systems are provided that comprise delivering first and second pulses of at least a first biphasic shock, wherein a parallel-series reconfiguration circuit connects and configures the capacitors of the capacitor bank in a parallel configuration to deliver a parallel biphasic shock； connecting the capacitors of the capacitor bank in a series configuration； and delivering first and second pulses of a second biphasic shock while the capacitors are connected in series to deliver a series biphasic shock.
