The effects of epinastine hydrochloride and terfenadine on electrocardiographic (ECG) parameters in rats were investigated from a pharmacokinetic and pharmacodynamic perspective. Epinastine hydrochloride (1 or 3 mg kg-1 h-1) or terfenadine (5, 10 or 15 mg kg-1 h-1) was intravenously infused into rats anaesthetized with urethane and alpha-chloralose. The changes in the QT interval derived from limb lead II and the chest lead, heart rate and PR interval were analysed. The time-course of the plasma drug-concentration of each drug was also investigated. Terfenadine prolonged the QT interval in an infusion-rate-dependent manner, its EC50 value was 792-1039 ng mL-1. An obvious QT prolongation was, moreover, observed even at a plasma terfenadine concentration of 100-200 ng mL-1, which is clinically quite high, but might be achieved under a definite condition such as a restrained terfenadine metabolism. Terfenadine also induced PR prolongation and bradycardia in an infusion-rate dependent manner. Epinastine slightly increased the heart rate, but did not affect any of the other ECG parameters even at a plasma concentration of 400 ng mL-1, which is more than 10 times the maximum concentration attained after an ordinary dosage regimen in man. We conclude that epinastine might have an advantage over terfenadine in avoiding adverse electrocardiographic reactions.