Diastolic heart failure affects approximately 40%-50% of patients presenting with signs and symptoms of heart failure. The aim of this study was to investigate the relationship between brain natriuretic peptide (BNP) levels and functional capacity in patients admitted with dyspnea and diagnosed with isolated diastolic dysfunction. Fifty-four patients (mean age, 57.4 +/- 8.5 years) with class-2 dyspnea with isolated diastolic dysfunction were enrolled. Serum levels of BNP were measured, and peak oxygen consumption (peak VO(2)), anaerobic threshold (AT), and metabolic equivalent (MET) values were determined with a cardiopulmonary exercise test (CPET). There was a negative correlation between BNP levels and exercise duration (P < 0.05, r = -0.304), AT (P < 0.05, r = -0.380), and number of MET (P < 0.05, r = -0.322) determined by CPET. When patients were divided into 2 groups according to BNP levels; BNP < or = 50 pg/mL (n = 40) versus BNP > 50 pg/mL (n = 14) and analyzed, those with BNP levels > 50 pg/mL had lower peak VO(2) (P = 0.05) and anaerobic threshold (P = 0.01) compared with patients with BNP < or = 50 pg/mL. The results suggest that BNP levels provide an indication about the functional capacity determined by CPET in patients admitted with dyspnea and isolated diastolic dysfunction.