A defibrillator is a similar device like a pacemaker but usually larger in size. It can restore normal heartbeat/heart rhythm by sending an electric pulse or shock to the heart. Defibrillators have been useful in preventing sudden death in patients with severe heart damage or in patients known to have irregular heart rhythms such as ventricular tachycardia or ventricular fibrillation. Defibrillator is inserted in a similar fashion to a pacemaker.