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The relationship between impaired baroreflex sensitivity (BS) and the degree of sympathetic activation during exercise in patients with heart failure (HF) has not been studied in detail. For this purpose, we studied BS and measured plasma norepinephrine (NE) at rest, and during and after treadmill exercise in 15 patients and 10 controls. HF patients showed lower BS in comparison to controls (3.51 ± 3.62 vs. 9.74 ± 4.56 ms/mm Hg; p < 0.001), and higher levels of plasma NE at rest (449.3 ± 147.1 vs. 261.1 ± 82.48 pg/ml; p < 0.001) and during exercise (1,542 ± 361.2 vs. 524.6 ± 92.61 pg/ml; p < 0.001). BS was directly related to pVO2 (r = 0.62; p = 0.0008) and inversely related to NE at peak exercise and to the increase in NE during exercise (r = 0.59, p = 0.005, and r = 0.53; p = 0.0058). Thus, during exercise, a marked sympathetic activation exists in patients with moderate HF. The relationship between increased plasma NE during exercise and decreased BS suggests that impaired baroreceptor function may be present in sympathetic activation in HF patients.