cTnI-ND does not alter the optimal resting SL in papillary muscles and the slack SL in isolated cardiomyocytes. (A) The longitudinal sections of LV papillary muscle fixed at the length of maximum force development and quantitative measurements showed that cTnI-ND,Tnni3^−/− and WT cardiac muscles have similar optimal resting SL. (B) The representative micrographs and quantitative analysis show that cardiomyocytes isolated from adult cTnI-ND,Tnni3^−/− and WT mouse hearts have similar SL in the presence of 10 mM BDM and absence of external load. 25–30 cells were measured from each heart. Values are mean ± SEM. n = 4–7 mice each in WT and cTnI-ND,Tnni3^−/− groups. Statistical analysis was done using Student’s t test, and no significant difference was found.