Comparison of sarcomere organization and cell contraction in iPSC-derived, neonatal, and adult CM. (A) Representative PALM images of the α-actinin network of investigated cell types. (B) Quantitative evaluation showed high similarity in z-disc thickness between iPSC, neonatal and adult CM (iPSCs vs. neonatal vs. adult: 73.45 ± 1.24 vs. 72.12 ± 1.56 vs. 74.6 ± 1.85). Likewise, no difference was detected for sarcomere length in iPSC-derived CM and neonatal cells (iPSCs vs. neonatal: 1.85 ± 0.046 vs. 1.84 ± 0.036), while adult CM demonstrated increased distances between individual sarcomere filaments (1.91 ± 0.01). (C) Contraction capacity was found to be similar in both iPSC-derived and neonatal CM. However, if contraction data were normalized to cell size, a reduced beating movement was measured in iPSC CM. Data are presented as mean ± SEM, n = 20 iPSC and neonatal CM, n = 10 adult CM. Statistical significance was determined using the one-way ANOVA and Student’s t-test. * p < 0.05. Scale bar 10 µm.