Moricizine chlorhydrate (Ethmozine), a relatively unknown antiarrhythmic agent in France, is a derivative of Phenothiazine, related to the Vaughan-Williams Class IB drugs. A randomised, double-blind, crossover trial with Disopyramide 600 mg/day after a placebo period in 10 patients with ventricular extrasystoles, half of whom had underlying cardiac disease, showed that moricizine 750 mg/day significantly reduced (p less than 0.05) the overall number of ventricular extrasystoles by 81 +/- 46% (disopyramide 72 +/- 69%; NS) and that this drug is effective in 2/3 of patients by suppressing 70 to 100% of ventricular extrasystoles, whereas disopyramide was effective in only 40% of the same patients and never gave better results than Moricizine. Cardiac and extracardiac tolerance of Moricizine was good in this study, confirming previously reported results and its superiority when compared with disopyramide (20% of unwanted effects in this series).