BACKGROUND Celivarone, a new noniodinated benzofuran derivative pharmacologically related to dronedarone and amiodarone, has been shown to have antiarrhythmic properties at a molecular level. The purpose of the 2 trials presented here (MAIA and CORYFEE) was to assess celivarone efficacy in the maintenance of sinus rhythm postcardioversion and for the conversion of atrial fibrillation (AF)/atrial flutter (AFL). RESULTS In the MAIA trial, 673 patients with AF/AFL recently converted to sinus rhythm were randomly assigned to receive 50, 100, 200, or 300 mg once-daily dosing of celivarone; 200 mg daily of amiodarone preceded by a loading dose of 600 mg for 10 days; or placebo. At 3 months' follow up, no significant difference was observed in time to AF/AFL relapse among the various celivarone groups and placebo. However, fewer symptomatic AF/AFL recurrences were observed in the lower-dose celivarone groups (26.6% for celivarone 50 mg [P = 0.022] and 25.2% for celivarone 100 mg [P = 0.018] vs 40.5% for placebo at 90 days). Fewer adverse events were observed with the use of celivarone and placebo than amiodarone. In the CORYFEE study, 150 patients with AF/AFL were randomly assigned to once-daily celivarone dosing of 300 or 600 mg, or placebo, for a 2-day treatment period. There was no significant difference in the rate of spontaneous conversion to sinus rhythm between the treatment and control groups. CONCLUSIONS In these studies, celivarone does not appear to be efficacious in the maintenance of sinus rhythm in AF/AFL patients or for the conversion of AF/AFL patients.