What patient conditions require immediate cardioversion?

More. There are really two types of electrical shock to the heart. Synchronized cardioversion is used to convert a rhythm that generally is still allowing blood flow out of the heart. Defibrillation is used to revive a heart that has either ventricular fibrillation or ventricular tachycardia and there is no or very low blood flow. Cardioversion times the event with the heart rhythm also.