Fig. 2.

Effects of a simultaneous infusion of ZD and ryanodine in the absence of Iso (n = 4). A: pseudo-ECG during simultaneous ZD and ryanodine infusion for 30 min showing 2 episodes of sinus pauses. B: isochronal maps of the first (a) and last (b) spontaneous beats originated from the middle SAN. The SAN is outlined with a dashed line. C: comparison of the first and last CLs between pauses. The mean CL of the first beat after the pause was significantly shorter than that of the last beat (P = 0.001).