ICH S7B guideline1 regulates in vitro IKr assay (such as hERG safety assay) and in vitro QT assay for identifying and assessing the potential of a test compound to delay ventricular repolarization. Ventricular repolarization is a complex physiological process determined by the duration of the cardiac action potential. It is the net result of the activities of many highly interdependent membrane ion channels and transporters. Many compounds can affect the activities of the ion channels or transporters, thus have the potential of delaying the ventricular repolarization and leading to prolonged QT interval.