EAD amplitude is sensitive to changes in the slope of the steady-state voltage dependence of activation of I_Ca,L. (A) Under dynamic clamp and in the presence of H₂O₂, we evaluated the effects of varying the slope factor (k) of the steady-state activation curve. Steady-state inactivation properties were unperturbed, whereas the slope of the steady-state activation curve was varied under dynamic clamp from k = 1 mV to k = 8 mV. The set of curves in the center, k = 4 mV, corresponds to the native I_Ca,L modified by H₂O₂. (B) Representative APs obtained for each k value studied, displaying EADs. For each value of k tested, the mean EAD amplitude (C), EAD occurrence (D), and APD₉₀ (E) are shown. Data from individual cells are shown as closed circles, and the means for all experiments are plotted as an open rectangles (n = 5–6 cells from five to six rabbits). Error bars indicate SEM. *, instances when the AP failed to repolarize before the next pacing stimulus are reported as RF (repolarization failure). Note that EAD amplitude grows as k is increased (slope becomes shallower).