Treatment of human iPSC-CMs (SCVI-273) with a maturation media containing triiodothyronine (10 nM), dexamethasone (1 μM), oleic acid (30 μM), and palmitic acid (80 μM) for 6 days promoted the maturation of iPSC-CMs. a, qPCR analysis of maturation markers in iPSC-CMs with or without the maturation treatment. n = 3 technical replicates. Unpaired Student’s t-test. b, Western blot analysis of OXPHOS proteins in EHTs with or without the maturation treatment, including NDUFB8, SDHB, ubiquinol-cytochrome c reductase core protein 2 (UQCRC2), MTCO2, and ATP5A. n = 4 EHTs per group. Unpaired Student’s t-test. c, Measurement of oxygen consumption rate (OCR) of iPSC-CMs with or without the maturation treatment. n = 17 wells. 10,000 cells/well. Two-tailed Mann–Whitney test. d, Analysis of calcium handling using Fluo-4 dye in iPSC-CMs with or without the maturation treatment. n = 31 immature cells and n = 30 mature cells. Two-tailed Mann–Whitney test. e, Contractility analysis of EHTs with or without the maturation treatment. n = 8 EHTs per group. Two-tailed Mann–Whitney test. For a, b, and e, data were normalized against the untreated cells or EHTs. Data are displayed as mean ± s.e.m.