Flecainide (F) is a new antiarrhythmic agent recently introduced into clinical practice. The above study was aimed at evaluating its intravenous (iv) pharmacokinetics in patients (pts) with acute myocardial infarction (AMI) on 1st and 2nd day, complicated by complex ventricular premature beats (VPBs). 2 mg/kg F was given iv as bolus injection, followed by 300 mg/24 hrs iv infusion. Plasma F values were evaluated by HPLC. Plasma F levels increased progressively, in a non uniform but predictable manner: in pts with large AMI and cardiac failure, F plasma levels, although remaining within the therapeutic range, were greatly increased after the 2nd hour (P less than 0.05) in comparison with pts without cardiac insufficiency. Negative side effects, both cardiac and extracardiac, were not observed: F appeared a handy and effective agent in post-AMI arrhythmias, especially when plasma drug levels are controlled; plasma F level monitoring is anyway recommended in pts with cardiac failure, owing to the wide interindividual variations.