**Figure 3.** **Assessment of phenotypes in FRDA iPSC-derived cardiomyocytes. (A)** Beating rates (beats per minute, BPM), **(B)** corrected extracellular field potential durations (cFPD) and **(C, D)** the root of the mean of the sum of the square of the difference in the RR interval (RMSSD) (ms). Data shows RMSSD at basal (**C**) and 10^{-6}M (**D**) isoprenaline ± nifedipine (NIF). **(E)** Representative Ca^{2+} transients. **(F)** Diastolic, **(G)** systolic and **(H)** amplitude Ca^{2+} in Control and FRDA- cardiomyocytes. (**A-D**) Data are mean ± SEM of combined values of 3 clones of each line (n=3 per line) and as a pool of all 3 clones of all FRDA lines (n=9 FRDA independent samples) and control cardiomyocytes (n=6). (**F-H**) Data are mean ± SEM of combined values of control cardiomyocytes (n=5), all 3 clones of each FRDA line (n=8-14 per line) and as a pool of all 3 clones of all FRDA lines (n=35 FRDA independent samples). Statistics: (**A-D, F-H**) One-way ANOVA followed by Bonferroni’s multiple comparison test, * p<0.05, **, p<0.01, ***, P<0.001.