The effect of hydroxyzine on action potentials in isolated guinea pig ventricular myocytes. (A) Superimposed action potentials recorded before and after exposure to various concentrations of hydroxyzine. (B) Concentration- and time-dependent prolongation of action potential duration at 90% (APD90). At each experimental condition (after exposure to 0.2 μmol/L for 5 min, 0.2 μmol/L for 10 min, 2 μmol/L for 5 min, and 2 μmol/L for 10 min), the APD90 values were normalized to control APD90 (obtained in the absence of drug). bP<0.05. n=4−9.