Stopping the heart is no problem --- that's what defibrillators do, after all! The heart stops, and then starts again with all its muscles in sync. The problem

Stopping the heart is no problem --- that's what defibrillators do, after all! The heart stops, and then starts again with all its muscles in sync. The problem is when the shock is not enough to stop the heart but causes it to lose sync and go into fibrillation.