A, representative records of IHERG, after P/4 leak subtraction, (upper traces) activated by ventricular action potential command (lower trace), in control and in the presence of 5 mm 4-AP. B, effect of 5 mm 4-AP on action potentials from guinea-pig ventricular myocytes. C, effect of 4-AP on resurgent IK tails from a guinea-pig ventricular myocyte (upper traces; lower trace shows a section of the voltage protocol. A mean inhibition of 71.1 ± 4.3 % was observed (n = 6).