Background Celivarone is a new antiarrhythmic agent developed for the treatment of ventricular arrhythmias.This study investigated the efficacy and safety of celivarone in preventing implantable cardioverter-defibrillator (ICD) interventions or death.Methods and Results Celivarone (50,100,or 300 mg /d) was assessed compared with placebo in this randomized,double-blind,placebo-controlled,parallel-group study.Amiodarone (200 mg /d after loading dose of 600 mg /d for 10 days) was used as a calibrator.A total of 486 patients with a left ventricular ejection fraction ≤ 40% and at least 1 ICD intervention for ventricular tachycardia or ventricular fibrillation in the previous month or ICD implantation in the previous month for documented ventricular tachycardia /ventricular fibrillation were randomized.Median treatment duration was 9 months.The primary efficacy end point was occurrence of ventricular tachycardia /ventricular fibrillation-triggered ICD interventions (shocks or antitachycardia pacing) or sudden death.The proportion of patients experiencing an appropriate ICD intervention or sudden death was 61.5 % in the placebo group;67.0 %,58.8%,and 54.9 % in the celivarone 50-,100-,and 300-mg groups,respectively;and 45.3 % in the amiodarone group.Hazard ratios versus placebo for the primary end point ranged from 0.860 for celivarone 300 mg to 1.199 for celivarone 50 mg.None of the comparisons versus placebo were statistically significant.Celivarone had an acceptable safety profile.Conclusions Celivarone was not effective for the prevention of ICD interventions or sudden death. Background Celivarone is a new antiarrhythmic agent developed for the treatment of ventricular arrhythmias. This study investigated the efficacy and safety of celivarone in preventing implantable cardioverter-defibrillator (ICD) interventions or death. Methods and Results Celivarone (50, 100, or 300 mg / d) was assessed compared with placebo in this randomized, double-blind, placebo-controlled, parallel-group study. Amiodarone (200 mg / d after loading dose of 600 mg / d for 10 days) was used as a calibrator. A total of 486 patients with a left ventricular ejection fraction ≤ 40% and at least 1 ICD intervention for ventricular tachycardia or ventricular fibrillation in the previous month or ICD implantation in the previous month for documented ventricular tachycardia / ventricular fibrillation were randomized. Median treatment duration was 9 months. The primary efficacy end point was occurred of ventricular tachycardia / ventricular fibrillation-triggered ICD interventions (shocks or antitachycard ia pacing) or sudden death. The proportion of patients experiencing an appropriate ICD intervention or sudden death was 61.5% in the placebo group; 67.0%, 58.8%, and 54.9% in the celivarone 50-, 100-, and 300-mg groups , respectively; and 45.3% in the amiodarone group.Hazard ratios versus placebo for the primary end point ranged from 0.860 for celivarone 300 mg to 1.199 for celivarone 50 mg. None of the comparisons versus placebo was significant significant. Celivarone had an acceptable safety profile .Conclusions Celivarone was not effective for the prevention of ICD interventions or sudden death.