QTempo assay allows analysis of the full range of ion channels. QTempo directly measures not only QT interval, but also a range of other cardiac action potential parameters (such as beat rate and the QRS complex). QTempo identifies compounds that affect Na, K and Ca ion channels and reflects their complex interactions. The cardiomyocyte clusters used in QTempo generate robust, consistent data over extended periods. This allows a wide variety of drug concentrations to be sequentially tested, increasing confidence in drug safety before further development.