Unfortunately, many non-cardiac drugs have also been reported to cause cardiac events including QT prolongation and/or life-threatening Tosade de points (TdP). Recent reports are shown that the diabetic patients with more pronounced QT abnormalities and cardiovascular complications. Repaglinide is well-known antidiabetic drug. Therefore, it is important that the evaluation of the potential effects of repaglinide on cardiac repolarization. In the present study, we examined the in vitro action potential (AP) assay with isolated rabbit Purkinje fiber (New Zealand White rabbits, 2.5-3 kg) to predict the potential of repaglinide to induce these undesirable adverse effects on the heart. Furthermore, we examined the effects of repaglinide on the major cardiac ion channels transiently transfected with the hERG(IKr), KCNQ1/KCNE1(IKs), KCNJ2(IK1) and SCN5A(INa) cDNA in HEK293 cells and the native voltage-gated Ca2+ channels in rats (Sprague-Dawley, 250-350 g, male) ventricular myocytes using the whole-cell patch clamp technique. Pooled data are expressed as means ± S.E.M., and compared by ANOVA followed by Dunnett’s test. According to the results, repaglinide at 30 μM significantly prolonged the action potential duration at 50% levels of repolarization (APD50, from 156.2 ± 4.3 to 179.1 ± 4.3 ms, n=4, P<0.05) and the action potential duration at 90% levels of repolarization (APD90, from 241.6 ± 7.4 to 278.9 ± 4.5 ms, n=4, P<0.01). According to ion channel studies, these effects could be induced by K+ channels blocking especially hERG and IKs. However, repaglinide at 100 μM significantly shortened the APD50 (156.2 ± 4.3 to 120.0 ± 7.9 ms, n=4, P<0.01) and APD90 (from 241.6 ± 7.4 to 190.9 ± 8.6 ms, n=4, P<0.01). In addition, the 100 μM repaglinide caused decrease of the maximum velocity of phase 0 (Vmax) from 269.2 ± 13.1 to 179.8 ± 9.1 V/s (n=4, P<0.01). These effects could be induced by the blocking of depolarizing currents for Na+ and Ca2+ channels. In the ion channel studies, repaglinide did inhibit the all of the tested ionic currents in a concentration-dependent manner except IK1. Among these ion channels, the voltage-gated Ca2+ channel was the most susceptible to repaglinide. The drug-induced shortening of the QT interval could potentially increase the ventricular tachycardia and the ventricular fibrillation risk of sudden death. Therefore, all patients taking this drug should be more carefully monitored for cardiac events.