During the past decade, a number of non-cardiovascular drugs have had their label revised or have been withdrawn from the market because of unexpected post-marketing reports of sudden cardiac death associated with a prolongation of the QT interval, and an increased propensity to develop a ventricular tachyarrhythmia called Torsades de Pointes. Although a direct link between QT interval prolongation and arrhythmogenesis is still unclear, QT prolongation is now the subject of increased regulatory review and is considered a significant risk factor for predicting human safety of New Chemical Entities. Consequently, pharmaceutical companies are striving to improve the drug discovery and development process to identify, as early as possible, the risk of novel agents, or their metabolites, of causing QT interval prolongation and to make appropriate go/no-go decisions or modify their development programme accordingly.