Cardiac toxicity due to the production of arrhythmias has previously been the most common reason for drugs to be withdrawn from the market or abandoned during development. The development of guidelines for the testing of the arrhythmogenic potential of drugs has led to testing that has been successful in preventing the development of drugs with cardiotoxic potential, but this has come at a high cost and attrition of a large proportion of new therapies due to a lack of sensitivity. New techniques are now being refined that allow the simultaneous assessment of a wide range of cardiac ion channels in cardiomyocytes derived from stem cells, which are cheaper to perform and allow a more comprehensive and sensitive analysis of the potential of drugs to induce serious arrhythmias. It is anticipated that these techniques will form the basis of new testing guidelines currently being developed.