Ventricular fibrillation
In patients who are very likely to keep having ventricular fibrillation, a special defibrillator can be put into their chest by a surgeon.  (This special defibrillator is called an "implantable cardioverter-defibrillator.")  Any time the person goes into ventricular fibrillation, the defibrillator will give the person's heart an electric shock, to bring the heart back into a normal rhythm.