Abstract: AIM: To determine the ionic basis of antiarrhythmic action of artemisinin. METHODS: The effects of artemisinin on the inward rectifier K current (I_k1) in isolated rabbit myocytes were studied using whole cell voltage clamp technique, and its effects on the cloned inward rectifier K channels (K_ir2.1) expressed in xenopus oocytes were investigated by two microelectrode voltage clamp technique. RESULTS: In rabbit myocytes, artemisinin significantly decreased Ik1 in a concentration-dependent manner. Artemisinin (50 μmol.L^-1) decreased Ik1 from -2.36±0.39 nA to -1.43±0.31 nA (P<0.05, n=6) at -100 mV. Artemisinin reduced the current of K_ir2.1 channel in xenopus oocytes in a dose-dependent and voltage-dependent manner when artemisinin was perfused with different concentration after K_ir2.1 cRNA was injected. The blockade effect of artemisinin on K_ir2.1 channel was revertible. CONCLUSION: Artemisinin inhibited effectively I_k1 in isolated rabbit myocytes. The mechanism of antiarrhythmic action of artemisinin may be related to its inhibition on I_k1 and blockade of K_ir2.1 channel current.