Sudden cardiac death accounts for approximately half of all cardiovascular mortality in the industrialized countries and ventricular tachyarrhythmia is the most common mechanism for this event. Implantable cardioverter-defibrillator (ICD) has been effectively used for prevention of sudden cardiac death in patients with life-threatening ventricular tachyarrhythmias since 1980. Clinical experience with ICD device now exceeds 100,000 implants worldwide and the number of implantation is increasing. In Korea, there is also increasing trend of ICD implantation. The authors report the initial experience of of ICD implantation in 6 patients who had high risk of sudden cardiac death.