We treated 13 children aged 0.2 years to 15.7 years (median 7.1 years) with flecainide acetate for refractory symptomatic supraventricular tachycardia. Six children had direct atrioventricular accessory pathways, of whom four had overt Wolff-Parkinson-White syndrome on the 12 lead electrocardiogram, while in the other two the accessory pathway was concealed. Three children had nodal atrioventricular re-entrant tachycardia, two had a re-entrant tachycardia, the exact mechanism of which was not known, one child had ectopic atrial tachycardia, and one had atrial flutter associated with an atrial septal defect. The remaining 12 children had structurally normal hearts. Flecainide (2 mg/kg intravenously) resulted in termination of the tachycardia in 11 of the 12 children treated during tachycardia. In 11 of the children successful prophylaxis was achieved with oral flecainide. Side effects occurred in two children during intravenous administration, but there were no side effects with oral treatment. This experience indicates that flecainide, which has not been used extensively in children, is an effective and safe antiarrhythmic agent, capable of terminating and controlling supraventricular tachycardia in children. Furthermore, flecainide may be successful where conventional agents fail.