Implantable defibrillator surgery. Surgeon unpacking during surgery to fit a biventricular implantable cardioverter-defibrillator (ICD). An ICD is used to treat serious ventricular arrhythmias (abnormal heart rhythm). It delivers an electrical shock that resets the heart rate to a normal rhythm. The main body of the ICD sits just under the skin and is attached to wires implanted into the heart muscle.