W e investigated the effects of a hot-water extract of Artemisia iwayomogi, a plant belonging to family Compositae, on cardiac ventricular delayed rectifier K + current (IK) using the patch clamp technique.The carbohydrate fraction AIP1 dose-dependently increased the heart rate with an apparent EC50 value of 56.1±5.5 μg/ml. Application of AIP1 reduced the action potential duration (