The hERG (human Ether-à-go-go Related Gene) encodes potassium channels that are responsible for the normal repolarization of the cardiac action potential. Blockage or any other impairment of these channels in heart cells can lead to fatal cardiac arrhythmias associated with prolongation of the QT interval. Druginduced blockage of potassium channels has been a major concern for the pharmaceutical industry, contributing to half of the safety-related recalls of drugs from the market since 1997 and impacting all therapeutic drug classes. Testing for hERG blockage, EADs and Torsades de Pointes are now mandatory for pharmaceutical discovery and development groups.