ENCAINIDE, a benzanillide derivative, is a new antiarrhythmic agent recently shown to have great efficacy in suppressing ventricular ectopy.` Initial electrophysiologic studies in animals have shown that encainide decreases automaticity, reduces the upstroke velocity and duration of the cardiac action potential and concurrently prolongs the effective refractory period of the action potential.' Subsequent studies have shown that encainide is effective in suppressing atrial and ventricular arrhythmias in a variety of species with varying experimental interventions.2'3 This study was designed to prospectively investigate the effectiveness of encainide given orally every 6 hours in reducing the frequency of ventricular premature complexes (VPCs) as confirmed on frequent ambulatory electrocardiographic recordings, serial exercise tests and invasive electrophysiologic tests. To minimize the effects of spontaneous variability on VPC frequency,8-10 patients with chronic, high