MMP9 and cardiac arrhythmia: Upon subjecting the hiPSC-CMs to high Ca2+ (3.6 mM)23, 26, irregular calcium transients that mimicked arrhythmia were induced after Ang II treatment, although these transients were almost absent in control hiPSC-CMs and in those treated with MMP-9 or PKA inhibitors (Fig. 5I–K).