Cyclic AMP responses were measured in adult rat ventricular myocytes using genetically-encoded FRET-based biosensors based on type II PKA which indexes cAMP in type II PKA domains including caveolae (left hand panels) and Epac2 without its tethering sequence which indexes cAMP in the global cytosolic compartment (right hand panels). Time course of changes in FRET response and pseudocolor images recorded under control conditions (a), and following exposure to submaximally (b) and maximally (c) stimulating concentrations of the β1-AR agonist isoproterenol (Iso). Control cells (A); MBCD-treated cells (B); Average changes in FRET responses (C). **P < 0.05, ns = not significant, n = 5-7. All Iso responses were blocked by the β1-AR antagonist CGP20712A (100 nM), but not by the β2-AR antagonist ICI118,551 (100 nM). Adapted from [41].