Figure 8. Action potential amplitude (AP amp; top) and maximum upstroke velocity (Vmax; bottom) as a function of pacing frequency.

White circles, wild type mice (n = 7); black circles, Scn5a ^+/− mice with a mild phenotype (n = 6); black triangles, Scn5a ^+/− mice with a severe phenotype (n = 5). At 800 bpm, 4 preparations from Scn5a ^+/− mice with a severe phenotype were periodically (for 1 of them) or continuously (for the 3 others) in 2∶1 conduction block. *, p<0.05.