The antiarrhythmic activity of flecainide has been tested in seven old patients (mean age 71 years) suffering from recurrent episodes of ventricular tachycardia. A basal 24-hour dynamic electrocardiogram was recorded for each patient and was repeated on day 5 of oral flecainide treatment (200 mg). A significant reduction (p less than 0.0001) of premature ventricular beats, of bigeminism (p = 0.0025) and of the episodes of ventricular tachycardia (p = 0.017) was obtained with plasma flecainide levels between 322 and 614 ng/ml. In addition, sinus rhythm was restored in two patients with stable atrial fibrillation and in the others ectopic atrial beats were markedly reduced. Among the ECG parameters examined, only QRS was significantly increased (p = 0.034). No significant change of blood pressure and laboratory parameters was observed. Untoward side effects were not observed.