We use quantitative phase digital holographic microscopy (QP-DHM) to image and quantify the beating movement of cardiomyocytes, derived from induced pluripotent stem cells (iPSCs), in control and drug-treated conditions. The development of an analysis algorithm has allowed extracting from the recorded quantitative phase signal (QPS) a set of several parameters that can efficiently characterize the cardiomyocytes beating patterns. Based on this approach, we monitored the effects of E-4031 (a class III antiarrhythmic drug) and isoprenaline (a common medication for bradycardia and heart block problems) on the cardiomyocyte beating patterns. Our results show that some effects specific to the mode of action of the drugs used can be identified. This stresses that QP-DHM can represent a promising label-free approach to identify new drug candidates by measuring their effects on iPSC-derived cardiomyocytes.