Effects of PI-103 and Iso on mouse heart rate ex vivo. (A) Representative tracings of cardiac electrical activity recorded from spontaneously beating hearts mounted on a Langendorff apparatus. Hearts were treated for 30 min with vehicle or 1 µM PI-103 (n = 3 per group) added to the perfusate, then for 30 min with or without 10 µM Iso. (B) Summary graph of heart rate shows mean ± SEM. Vehicle − Iso versus + Iso, P = 0.001; PI-103 − Iso versus + Iso and vehicle − Iso versus PI-103 − Iso, P = 0.03; vehicle + Iso versus PI-103 + Iso, P = 0.20; Student’s t test.