ABSTRACTThis was a prospective, placebo-controlled, single-blind trial of moricizine (ethmozine) in a dose averaging 10 mg/kg/day in 50 patients, the single entrance criterion being the presence of lO or more runs of nonsustained ventricular tachycardia (VT) on a screening 24 hr ambulatory electrocardiographic (ECG) recording. Electrophysiologic study was not included as part of this trial design. The placebo frequency of VT (average 3 days of recording) was 1036 + 479 runs of VT per day. Most patients (31/50) had coronary artery disease. The study population had a mean left ventricular ejection fraction (LVEF) of 36 ± 16%; 20 patients also had a history of sustained VT. Protocol failure was defined as failure to achieve a 75% or greater reduction in runs of VT (as judged by ambulatory ECG recording) and/or recurrence of sustained VT while on moricizine. Among the 48 patients treated with moricizine, the drug was initially efficacious in 35 (73%), with two-thirds having total abolition of nonsustained VT. Although it was effective in reducing runs of nonsustained VT, moricizine was ineffective in preventing the recurrence of sustained VT (63% failure rate). Side effects were uncommon and the drug was well tolerated in most patients with LVEFs of 30% or less.