A good example of ventricular fibrillation converted by electric defibrillation to what appears to be a sinus rhythm.  There is significant artifact in the post-conversion strip, but the last beat on the strip appears to have a P-QRS-T sequence.

Of course, V Fib presents without pulses, and must be defibrillated as soon as possible.  Best results are achieved by defibrillating a perfused heart, so if there is any delay from onset of V Fib, CPR should be performed to perfuse the heart prior to defibrillation.