After an initial pilot study in 5 patients, the effect of flecainide on chronic ventricular arrhythmias was tested during 48-h oral administration of 250 mg twice a day in 9 further patients with previously drug-resistant chronic, stable ventricular arrhythmias. Mean age was 45.9 .+-. 14.9 yr; 7 patients were male. Three patients had coronary artery disease, while the diagnoses in the remaining patients were congestive cardiomyopathy, aortic stenosis or no apparent heart disease. Continuous Holter monitoring with quantitative evaluation was performed in all patients for 24 h before and during a 2 days'' period of treatment. The mean number of ventricular ectopic beats decreased from 20.3 .+-. 6.4 beats/min during hour 6 of treatment and further to 3.1 .+-. 7.7 beats/min during hour 25-48 after onset of treatment. In 8 of 9 patients, the mean decrease in ventricular ectopic rate was 97.5%. In only 1 patient, therapy was ineffective. Ventricular couplets were completely suppressed in 6 of 8 cases. Looking at the spontaneous variability of ventricular ectopic beats during the control period, 8 of 9 patients showed a decrease which considerably exceeded the statistically necessary one. Headache of moderate degree was reported in 1 case in the pilot study. Therapy had to be stopped after the 1st dose because of QRS widening in another patient. In conclusion, this short-term study suggests that flecainide may be an effective drug for the management of ventricular arrhythmias.