Calibration with action potential (AP) data constrains currents affecting upstroke and resting potential, but current redundancy during repolarization allows wide ranges of variability in currents impacting AP duration (APD). A and B: selected pairwise plots of maximal conductances (A) and partial correlation coefficients (PCCs) between AP biomarkers and maximal conductances (B), computed at 0.25, 1, and 3 Hz, for the Maleckar-based population. C and D: analogous results for the Grandi-based population. In B and D, positive (+) and negative (−) correlations are highlighted.