Chronic treatment of HCM EHTs with mavacamten. (A) WT2 and HCM iPSC-CM cTnT immunostaining. (B) HCM iPSC-CMs had an ∼70% increase in cell size (P < 0.0001, t test). (C) BNP was upregulated in HCM iPSC-CMs (P = 0.0075, Mann–Whitney U test). (D) ERK activation was increased in HCM iPSC-CMs (P = 0.0123, t test). (E) BNP expression was significantly downregulated in HCM EHTs by this chronic mavacamten treatment (P = 0.0095, Mann–Whitney U test). (F) Treated and untreated WT2 and HCM EHTs (using two-way ANOVA, interaction P = 0.03) in PF was found to be significant, indicating that the chronic effect of mavacamten in decreasing cellular contractile force was greater in HCM EHTs than in WT2 EHTs. (G) WT2 and HCM iPSC-CM cTnT immunostaining with and without chronic mavacamten treatment. (H) Treated and untreated WT2 and HCM iPSC-CMs (using two-way ANOVA, interaction P < 0.0001) in cell size was found to be significant. Data are mean ± standard error. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001. ANP, natriuretic peptide A; au, arbitrary units.