In order to reduce cardiovascular safety liabilities of new therapeutic agents, there is an urgent need to integrate human-relevant platforms/approaches into drug development1. Optimizing baseline function of human induced pluripotent stem cell-derived cardiomyocytes (hiPSCCMs) is essential for their effective application in models of cardiac toxicity and disease2. Here, hiPSC-CMs were cultured on flexible substrates using the FLEXcyte 96 system. The promaturation environment enables observation of inotropic and chronotropic compound effects, which are typically hard to detect with 2D monolayers on overly stiff substrates3. For example, the beta-adrenergic agonist isoprenaline, or isoproterenol, is well known for its positive inotropic effects on the human heart, although common hiPSC-CM in vitro assays fail to display this physiological response by this compound.