The effect of drugs on cardiac electrophysiology is important in commercial screening for human drug development. Isolated tissue from animal models and non-muscle expression-systems are currently used to screen for potential pro-arrhythmic effects. Recently, human cardiomyocytes derived from induced pluri-potent stem cells (iPSCs) with an electrophysiological phenotype similar to the ventricular myocardium have become available commercially. This study investigated the sensitivity of these cells to a series of standard drugs, and compared responses to published effective therapeutic concentrations in humans. iPSC (obtained from Cellular Dynamics Inc, Madison WI), were maintained in culture for 10 days in a plastic 48 well plate. The cells were washed in serum-free medium and exposed transiently to 3 µM Di-4-ANEPPS. The plate was placed was placed in a stage incubator on an inverted microscope and the spontaneous electrical activity was recorded as the Di-4-ANEPPS fluorescence signal from areas of iPSCs in individual wells using a 40x (NA 0.6) objective. Fluoresence signals were digitized at 10kHz and the records subsequently analyzed off-line. Cells were exposed to cumulative increases in drug concentrations allowing 30 mins incubation at each concentration. The procedure was repeated up to 9 times and parallel measurements were done on cells with equivalent concentrations of vehicle. Incrementing the drug concentration by 0.5 log units, a threshold was established as the first concentration at which detectable differences between the drug and control group were observed. Action potential parameters were measured, including 10%-90% rise time (Trise) action potential duration at 75% duration (APD75). Drugs used in this study were: E4031, Mexiletine, Nifedipine. Data are expressed as % change from baseline for the drug and vehicle groups. Significant effects on APD75 were detected at 30nM E4031 vs. the control (40.0% vs. 3.2%, P<0.01 n=9). Mexiletine at 3µM significantly increased Trise (343.5% vs 134.8%, P<0.01 n=9, P<0.01 n=9). Nifedipine decreased APD75 (39.1% vs. 75.5%, P<0.05 n=4 P<0.05 n=4) at 300nM. The detection threshold for these drug effects co-incides with published values of effective therapeutic plasma levels: (E4031, 3nM, Fujiki et al (1994); Mexiletine 2-4µM, Harner et al (2011); Nifedipine, 4-8nM, Redfern et al (2003). In conclusion, iPS derived cardiomyocytes appear to show drug sensitivities that would make them an appropriate for an invitro screen for electrophysiological effects of compounds invivo.