We investigated the effect of flecainide on systolic time intervals in 6 healthy subjects. A randomized, double blind, cross-over study was designed using flecainide (2 mg/kg), propranolol (0.2 mg/kg) or saline. In comparison with placebo, flecainide increased heart rate, diastolic BP, QT-Index, QS2-Index, PEP, and reduced LVET-Index (p less than 0.05). It caused a significant increase in PR interval, QRS duration, and PEP/LVET (p less than 0.01). Propranolol, compared with placebo, decreased heart rate and systolic BP (p less than 0.05). It increased PR interval, PEP, and PEP/LVET ratio (p less than 0.05). In comparison with propranolol, flecainide increased heart rate and QRS duration (p less than 0.01, p less than 0.001 respectively). It increased diastolic BP, PR interval, QS2-Index, PEP, and PEP/LVET ratio, and decreased LVET-Index (p less than 0.05). These changes in STI induced by flecainide may be produced by depression of myocardial contractility. Intraventricular conduction delay may be an additional contributing factor.