Several proven medical therapies such as beta-blockers and angiotensin converting enzyme inhibitors play important roles in preventing sudden death of patients with heart failure. Therapy with amiodarone and therapy with implantable cardioverter defibrillator (ICD) have developed specifically to prevent sudden death by life-threatening arrhythmias. But recently many large-scale clinical trials have proved that ICD therapy improves prognosis of patients with heart failure better than amiodarone therapy. Because ICD is not a treatment to prevent the occurrence of ventricular arrhythmias, it may not necessarily improve quality of life of patients. In that respect catheter ablation may play a role in preventing life-threatening arrhythmias.