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Figure 2 The heart rate response to isoproterenol infusion in dilated cardiomyopathy (DCM) before (A) and during carvedilol (n = 5) or metoprolol controlled release/extended release (CR/XL) (n = 5) treatment (B) and in five control dogs with cessation of pacing alone. *p < 0.05 compared with carvedilol and metoprolol. (C) The adenylyl cyclase response to guanine triphosphate/isoproterenol (GTP/Iso) and sodium flouride in sarcolemmal membrane preparations from these same dogs obtained after euthanasia. *p < 0.05 compared with baseline. p < 0.05 compared with DCM. Carv = carvedilol; Con = control subjects; Iso = isoproterenol; Met = metoprolol.