A method of characterizing an effect of a compound on cardiomyocyte beating, including providing a system configured to culture, electrically pace, and monitor heating of beating cells: culturing two populations of immature cardiomyocytes in the system; adding a compound suspected of having an effect on cardiomyocyte maturation to one of the populations of immature cardiomyocytes; electrically pacing the two populations of immature cardiomyocytes according to a pulse profile that functionally matures immature cardiomyocytes until at least one of the two populations of cardiomyocytes is functionally mature; and Characterizing the compound as further driving maturation if the population with compound addition functionally matures before the other cardiomyocyte population.