 [ Symptoms ] what is an implantable cardioverter defibrillator icd [ Disease ] an icd is a sophisticated device used primarily to treat ventricular tachycardia and ventricular fibrillation two life threatening heart rhythms the icd constantly monitors the heart rhythm when it detects a very fast abnormal heart rhythm it delivers energy to the heart muscle to cause the heart to beat in a normal rhythm again there are several ways the icd can be used to restore normal heart rhythm they include anti tachycardia pacing atp when the heart beats too fast a series of small electrical impulses may be delivered to the heart muscle to restore a normal heart rate and rhythm cardioversion a low energy shock may be delivered at the same time as the heart beats to restore normal heart rhythm defibrillation when the heart is beating dangerously fast or irregularly a higher energy shock may be delivered to the heart muscle to restore a normal rhythm anti bradycardia pacing many icds provide back up pacing to maintain heart rhythm if it slows too much