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Although pulmonary arterial hypertension (PAH) and chronic heart failure (CHF) lead to exercise limitation, their pathophysiology is different. Our objective was to evaluate, using right heart catheterization and cardiopulmonary exercise testing, the difference in hemodynamic parameters and exercise capacity between PAH and CHF, which have the same subjective symptoms.We studied 20 PAH (mean pulmonary artery pressure: 36 ± 10 mmHg, all . 25 mmHg) and 20 CHF (ejection fraction: 35 ± 10%, all < 40%) patients who underwent both cardiopulmonary exercise testing and right heart catheterization. All patients were in New York Heart Association functional class II or III.Peak oxygen uptake (VO2) was lower for PAH patients than for CHF patients (11.7 ± 3.2 mL·kg21·min21 vs 14.5 ± 4.6 mL·kg21·min21, P = .03), while the slope of ventilation to carbon dioxide production ratio (VE/VCO2) was higher for PAH patients than for CHF patients (41.0 ± 12.7 vs 28.0 ± 9.0, P = .001), despite the similarity in their New York Heart Association functional class. Peak VO2 and VE/VCO2 correlated with cardiac index for both groups. An important finding was that peak VO2 correlated with pulmonary vascular resistance for PAH patients (r = 20.46, P = .04) but not for CHF patients (r = 0.33, P = .15). Furthermore, peak VO2 correlated with pulmonary capillary wedge pressure for CHF patients (r = 20.47, P = .03) but not for PAH patients (r = 0.17, P = .47), while the VE/VCO2 slope correlated with pulmonary capillary wedge pressure (r = 0.67, P = .002) but not with pulmonary vascular resistance (r = 0.12, P = .63) for CHF patients.Peak VO2 and VE/VCO2 slope were worse for PAH patients than for CHF patients despite the similar subjective symptoms. This difference might be explained by an altered hemodynamic status.