Abstract: The effects of the novel Kv1.5 channel blocker AVE 0118 on human atrial potassium currents (IKur, Ito and IK1) were investigated in this study. We could demonstrate that AVE 0118 blocks IKur not voltage dependent with an IC50 of 37 (5;270) nmol L-1 at +40 mV. Compared with IKur, Ito peak current was only slightly altered. At 30 μmol L-1 current amplitude was reduced by 31±6%, Ito inactivation time constant decreased from 33.9±2.0 ms to 10.0±1.9 ms resulting in a 73 ±5% reduction of total potassium flow through Ito. IC50 of the dose response relation of the reduction of Ito net current was 300 (100;1000) nmol L-1. There was only little effect of AVE 0118 on IK1, current was reduced only 11±3% at a concentration of 10 μmol L-1 at a test-potential of –90 mV. AVE 0118 is an antiarrhythmic substance with a new drug action mechanism. Drugs with an attenuated effect on Ikur and a (compared to the ventricle) stronger delay of the repolarization on the atrial level are therefore a new and interesting tool for treatment of supraventricular arrhythmias like atrial fibrillation.