Atrial selective electrophysiological effects of UCL1684 in the induction of PRR (A-D), reduction of Vmax (E-F), increase in DTE (G), and prolongation of the shortest S1-S1 interval permitting 1:1 activation (H). Composite data of Vmax of atrial and ventricular APs following acceleration from a CL of 500 to 300 ms expressed as % of Vmax value recorded at a CL of 500 ms in Controls (F).* p <0.05 vs. control. # - p<0.05 vs. respective ventricular value. N=7–10. Data presented in C, D, E, and G were obtained at a pacing CL = 500 ms.