A, control (left) and post-MI (right) APs were applied to myocytes after a loading protocol of eight 100 ms steps to +10 mV. B, kinetically corrected intracellular Ca2+ transients triggered by control and post-MI APs. These data were used to calculate the SR release flux, Frel, according to the equation: d[Ca2+]i/dt =Frel+Fpump+Fleak+Σd[CaL]/dt (see Methods). C, SR release flux, Frel, triggered by short control and long post-MI APs. D, rate of unloaded cell shortening, d(CS)/dt, triggered by control and post-MI APs.