An implantable cardioverter defibrillator having a plurality of high voltage capacitors in the output stage which are coupled in parallel and a switching matrix for controlling the number of capacitors used to deliver the shock. For patients having lower DFTs, the number of capacitors in the output stage, as controlled by the switching matrix, can be reduced thus reducing the capacitor charging time prior to delivering a defibrillation shock. Additionally, if one of the capacitors experiences a degradation in performance, it can be switched out of the output circuit as long as the remaining capacitors can provide the necessary energy delivery for defibrillation. In another embodiment of the invention, if a particular defibrillation shock is ineffective, the back-up capacitors may be switched into the high voltage output circuit for delivery of the next shock.