The main function of a defibrillator is to prevent sudden death and terminate VF with an electrical shock. This tracing illustrates the normal function of a defibrillator. The episode, diagnosed in the VF zone was properly detected and successfully treated with an electrical shock. The arrhythmia was immediately extremely rapid, polymorphous and disorganized. Any attempt at terminating this type of arrhythmia by ATP seemed futile, and an electrical shock was the therapy of choice. No discrimination of the arrhythmia origin is attempted in this rate range, despite the attempts by the device to find stability and sudden onset values. It is, however, noteworthy, that a stability analysis is applied in the decision to deliverer an ATP one shot. A series of defibrillating shocks is usually programmed in the VF zone. The strength of the first shock is programmed either at the maximum capable by the device (as in this case), or at a strength 10-J lower, or at a lower strength tested after the implant procedure. The higher the strength of the first shock, the longer the charge time and the longer the time between the onset of arrhythmia and the delivery of the shock. In this patient, the delay between the onset of arrhythmia and the shock was 14 sec, explaining the occurrence of syncope. The following shocks are usually programmed at a maximum strength. In the Biotronik defibrillators, the maximum number of shocks delivered for a given episode is limited to 8, with the last 6 necessarily at maximum strength. The likelihood of a successful shock after 8 failed attempts at maximum strength is, indeed, very low. The shock polarity (positive versus negative) can be alternated, starting with the first shock at maximum strength. On the other hand, the number of shocks must be limited in order to avoid a disastrous situation during the delivery of a series of inappropriate therapies.