It is well established that a depressed baroreflex sensitivity may adversely influence the prognosis in patients with chronic heart failure (CHF) and in those with previous myocardial infarction. We tested whether a slow breathing rate (6 breaths/min) could modify the baroreflex sensitivity in 81 patients with stable (2 weeks) CHF (age, 58+/-1 years; NYHA classes I [6 patients], II , III , and IV ) and in 21 controls. Slow breathing induced highly significant increases in baroreflex sensitivity, both in controls (from 9.4+/-0.7 to 13.8+/-1.0 ms/mm Hg, P<0.0025) and in CHF patients (from 5.0+/-0.3 to 6.1+/-0.5 ms/mm Hg, P<0.0025), which correlated with the value obtained during spontaneous breathing (r=+0.202, P=0.047). In addition, systolic and diastolic blood pressure decreased in CHF patients (systolic, from 117+/-3 to 110+/-4 mm Hg, P=0.009; diastolic, from 62+/-1 to 59+/-1 mm Hg, P=0.02). These data suggest that in patients with CHF, slow breathing, in addition to improving oxygen saturation and exercise tolerance as has been previously shown, may be beneficial by increasing baroreflex sensitivity.