The long-term clinical effect of oral flecainide treatment was evaluated in 107 pts (10-82 yrs). Indications for treatment were: atrial fibrillation 38%, atrial flutter 16%, ventricular tachycardia 24%, ventricular ectopic beats 10% and supraventricular tachycardia 12%. Daily flecainide dosage was 200 (100-400) mg. Follow-up period 3 mths (15 days-15 mths). Based on the history and ECG flecainide had been effective in 51 pts. The improvement was most pronounced in pts suffering from supraventricular tachycardia involving an accessory bypass tract (84-92%). Flecainide had been discontinued in 50 pts due to: insufficient effect in 28, side effects in 17 and for other reasons in 5. The side effects indicating flecainide withdrawal (pts) were: cerebral symptoms (4), gastrointestinal complaints (2), bradyarrhythmias (2), heart failure (3) and suspected pro-arrhythmia (4). (Ventricular tachycardia in 3, 1:1 AV-conducting during atrial flutter in 1).