(A) Experimental protocol. In the control and TRAP groups, all hearts were perfused with Krebs-Henseleit solution for 25 min just before TRAP was added in perfusion. After 15 min, TRAP (200 nmol/L) or TFA was washed out with Krebs-Henseleit solution. In the TRAP + 5HD group and TRAP + HMR1098 group, the hearts were perfused with Krebs-Henseleit solution for 10 min before 5HD or HMR1098, respectively, were perfused. Then, 15 min later, TRAP was perfused for another 15 min before being washed out. (B) Representative tracings measuring the electrophysiological effect of TRAP on the left ventricular walls. Each panel shows (from top to bottom) simultaneous recordings of the ECG recorded across the left ventricular, EpiMAP and EndoMAP (B1) The effect of TRAP (200 nmol/L). (B2) The effect of TFA. (C) Representative electrophysiological tracings showing the effect of TRAP (200 nmol/L) and HMR1098 on the left ventricular walls. (D) Representative tracings showing the electrophysiological effect of TRAP + 5HD.