(A–C) Correlative live-cell-immunofluorescence of CM dedifferentiation on (A) 2 MPa, (B) 20 kPa, and (C) 5 kPa matrices. Recently divided P1 Myh6-Cre;R26R-dTomato-lox CMs, following time-lapse imaging (A, B, C, left panel, and A′, B′, C′), correlated with the expression of cTnT (A′′, B′′, C′′), and Ki67 (A′′′, B′′′, C′′′). CMs following cell division are denoted with white arrows. (D) An overview of a field of P1 Myh6-Cre;R26R-dTomato-lox CMs (red, left panel), immunostained for cTnT (green, middle panel), and a merge of Tomato+/cTnT− images (right panel). Scale bar: 50 µm. (E) Quantification of Tomato+/cTnT− CMs on 2 MPa, 20 kPa, and 5 kPa (n = 19,869). (F) An overview of a field of P1 Myh6-Cre;R26R-dTomato-lox CMs (red, left panel), immunostained for MHC (green, middle panel), and a merge of the Tomato+/MHC− images (right panel). Scale bar: 20 µm. (G) Quantification of Tomato+/MHC− CMs on 2 MPa, 20 kPa, and 5 kPa substrates. Scale bar: 20 µm (n = 13,474). (H) P1 Myh6-Cre;R26R-dTomato-lox/cTnT− CMs expressing Nkx2.5. (I) Schematic diagram showing CM dedifferentiation from a mature to an immature proliferative state, facilitated by compliant matrices. Statistical significance was determined using ANOVA followed by post-hoc Tukey's (HSD) test. Results are marked with one asterisk (*) if p < 0.05.