['The goal of this study was to determine if brain natriuretic peptide (BNP) levels are associated with exercise capacity in patients with chronic heart failure (HF).', 'Plasma levels of BNP are increased subject to the degree of systolic and diastolic left ventricular dysfunction in patients with chronic HF. Exercise testing is useful to assess functional capacity and prognosis in chronic HF.', 'We prospectively studied 70 consecutive patients with chronic HF (60.3 +/- 10.4 years, 51 men) referred for cardiopulmonary exercise testing. Resting BNP was obtained after 10 min of supine rest before symptom-limited bicycle exercise testing.', 'In patients with chronic HF, BNP levels correlated with oxygen uptake (VO(2)), both at anaerobic threshold (VO(2)AT: r = -0.54, p < 0.001) and peak exercise (peak VO(2): r = -0.56, p < 0.001). Impairment of ventilatory efficiency (EqCO(2): r = 0.43, p < 0.001) and maximum exercise level (W % predicted: r = -0.44, p < 0.05) correlated less well with BNP. There was a significant inverse correlation between left ventricular ejection fraction and BNP (r = -0.50, p < 0.05). Brain natriuretic peptide discriminated well chronic HF patients with a peak VO(2) <10 ml/min/kg (area under the receiver operating characteristic [ROC] 0.93) or <14 ml/min/kg (area under the ROC 0.72). A BNP >316 pg/ml was associated with a risk ratio of 6.8 (95% confidence interval, 2.3 to 19.8) for a reduced exercise capacity with a peak VO(2) <14 ml/min/kg.'] Do brain natriuretic peptide levels predict functional capacity in patients with chronic heart failure?