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Figure 6 The receptor-active 61-residue recombinant neuregulin-1 peptide (rhNRG-1) improves cardiac functions in dogs with pacing-induced heart failure. Three groups of animals were studied (n = 6/group), as detailed in Methods. The control group (sham) had a pacing lead implanted, but animals in this group were not paced. The 2 experimental groups were paced at 230 beats/min for 3 weeks and then treated with either vehicle or rhNRG-1 (3 µg/kg/day, IV, for 5 days). Pacing was continued during the treatment periods. Heart rate (HR) (A), mean arterial pressure (MAP) (B), left ventricular (LV) end-systolic (white bars) and end-diastolic pressures (black bars) (C), and rates of LV contraction (+dP/dt, white bars) and relaxation (–dP/dt, black bars) (D) were determined after the treatment periods (i.e., after 26 days of pacing). Ejection fraction (EF, percent) (E) and cardiac output (F) were determined on 3 occasions: 1) after the recovery period immediately before pacing was commenced (black bars), 2) after pacing for 3 weeks (red bars), and 3) after 5 days of vehicle or rhNRG-1 treatment (blue bars). Pacing was discontinued at the time of the hemodynamic and cardiac contractility measurements. *p < 0.05; **p < 0.01 versus vehicle.