Fig. 5: Analysis of contractility and structural development.

a Analysis of beating rate. CMs of the MM + NP + ES group contracted with a beating rate of 120 BPM (beats per minute) during the presence of ES but regained spontaneous beating after ES was discontinued. n = 15 cultures/group of 5 independent differentiations of 3 iPSC lines. b Statistical analysis of beating properties: contraction time, relaxation time and beating duration of iPSC-CMs under 0.5 Hz field stimulation. n = 15 cultures/group of 5 independent differentiations of 3 iPSC lines. A schematic diagram of two beat traces showing how the parameters were analysed is shown in Supplementary Fig. 2a. c Heatmap of the ability of iPSC-CMs to adapt to increasing pacing frequencies from n = 15 cultures/group of 5 independent differentiations of 3 iPSC lines. The colour scale represents the number of cultures. Representative beating traces are shown in Supplementary Fig. 2b,c. d Expression of denoted marker genes for structural maturation. n = 7 (TNNI1, TNNI3, MYL2, MYL7) and 9 (MYH6, MYH7) independent differentiations of 3 iPSC lines. HPRT is used as a housekeeping gene. e Quantification of cell volume (FSC-A) and granularity (SSC-A) in the cTNT-positive CM populations using flow cytometry analysis. n = 18 independent differentiations/group of 3 iPSC lines. f, g Proportion of cTNT-positive cells (f) and quantification of mean fluorescence intensity of cTNT (g). n = 17 (f) and 11 (g) independent differentiations/group of 3 iPSC lines. Log transformation was performed for statistical analysis (g). The gating strategy used to analyse the flow cytometry data is shown in Supplementary Fig. 3. Symbols denote iPSC lines: circles for isWT7, squares for iWTD2, and triangles for iBM76. Source data are provided as a Source Data file. Statistical analysis was performed using Kruskal-Wallis test with Dunn’s multiple comparison test (b, d) and linear mixed model (two-sided) with Tukey’s correction for multiple comparisons between the 4 groups (e–f). Data are presented in box plots indicating median (middle line), 25th, 75th percentile (box) and min and max data points (whiskers).