cTnI-ND,Tnni3 ^−/− ex vivo working hearts show extended Frank-Starling response as compared to WT control. (A) The SDS-gel and mAb TnI-1 Western blot show the expression of solely cTnI-ND in the heart of adult cTnI-ND,Tnni3^−/− double transgenic mice. Age-matched WT C57BL/6J mouse heart was examined as control. Normal expression of cTnT in cTnI-ND,Tnni3^−/− mouse heart is shown by the mAb CT3 blot. MHC, myosin heavy chain. (B) The Frank-Starling response curves show that the stroke volume of cTnI-ND,Tnni3^−/− mouse hearts normalized to heart weight continued to increase when preload was raised above 10 mmHg whereas it was plateaued in WT hearts. The values are mean ± SEM. n = 5–6 mice in WT and 8–9 mice in cTnI-ND,Tnni3^−/− groups. *P < 0.05 and **P < 0.05 vs. WT at preload of 10–20 mmHg in two-way ANOVA with post-hoc method of Tukey test; ^aaaP < 0.001 vs. stroke volume at 10 mmHg preload; ^bP < 0.05 and ^bbP < 0.01 vs. stroke volume at 12.5 mmHg preload; ^ccP < 0.01 vs. stroke volume at 15 mmHg preload in paired Student’s t test. ↑ and ↓ indicate increase and decrease in the comparisons.