© 2018 The Authors. Rationale: Myofibroblasts are believed to evolve from precursor cells; however, whether noncardiomyocyte cardiac cells (NMCCs; ie, endothelial cells, smooth muscle cells, pericytes, and fibroblasts) that have been derived from human-induced pluripotent stem cells (hiPSCs) can transdifferentiate into myofibroblast-like cells, and if so, whether this process reduces the efficacy of hiPSC-NMCC therapy, is unknown. Objective: To determine whether hiPSC-NMCCs can differentiate to myofibroblast-like cells and whether limiting the transdifferentiation of hiPSC-NMCCs can improve their effectiveness for myocardial repair. Methods and Results: When endothelial cells, smooth muscle cells, pericytes, and fibroblasts that had been generated from hiPSCs were cultured with TGF-β (transforming growth factor-β), the expression of myofibroblast markers increased, whereas endothelial cell, smooth muscle cell, pericyte, and fibroblast marker expression declined. TGF-β-associated myofibroblast differentiation was accompanied by increases in the signaling activity of Smad, Snail, and mTOR (mammalian target of rapamycin). However, measures of pathway activation, proliferation, apoptosis, migration, and protein expression in hiPSC-endothelial cell-derived, smooth muscle cellderived, pericyte-derived, and fibroblast-derived myofibroblast-like cells differed. Furthermore, when hiPSCNMCCs were transplanted into the hearts of mice after myocardial infarction, ∼21% to 35% of the transplanted hiPSC-NMCCs expressed myofibroblast markers 1 week later, compared with <7% of transplanted cells (P<0.01, each cell type) in animals that were treated with both hiPSC-NMCCs and the TGF-β inhibitor galunisertib. Galunisertib coadministration was also associated with significant improvements in fibrotic area, left ventricular dilatation, vascular density, and cardiac function. Conclusions: hiPSC-NMCCs differentiate into myofibroblast-like cells when cultured with TGF-β or when transplanted into infarcted mouse hearts, and the phenotypes of the myofibroblast-like cells can differ depending on the lineage of origin. TGF-β inhibition significantly improved the efficacy of transplanted hiPSC-NMCCs for cardiac repair, perhaps by limiting the differentiation of hiPSC-NMCCs into myofibroblast-like cells.