Time courses of the effects of terfenadine, chromanol 293B and famotidine on the heart rate, PR interval, QRS width and QT interval, QTc(B) (corrected by Bazett's formula), QTc(F) (corrected by Fridericia's formula), QTc(V) (corrected by Van de Water's formula) and QTc(M) (corrected by Matsunaga's formula). The inset figures show QT–RR relationship. In the terfenadine group, predrug control values of the heart rate, PR interval, QRS width, QT interval, QTc(B), QTc(F), QTc(V), and QTc(M) were 177±10 beats min−1, 69±5, 24±5, 190±9, 325±7, 272±8, 247±7 and 208±7 ms, respectively (n=4), and terfenadine in doses of 0.3 and 3.0 mg kg−1 prolonged the QT interval by 23±6 and 89±19 ms, respectively. In the chromanol 293B group, the predrug control values were 196±13 beats min−1, 60±2, 22±2, 160±4, 287±6, 236±4, 220±3 and 178±3 ms, respectively (n=4), and chromanol 293B in doses of 0.1 and 1.0 mg kg−1 prolonged the QT interval by 14±7 and 33±8 ms, respectively. In the famotidine group, the predrug control values were 224±4 beats min−1, 61±3, 23±4, 162±4, 302±8, 245±5, 224±4 and 183±4 ms, respectively (n=4), and no significant change was detected after administration of famotidine. Data are presented as mean±s.e.m. The closed symbols represent the significant differences from each predrug control (C) value by P<0.05.