Oxygen transport capacity is the most important determinant of maximum oxygen uptake (V(O2) max) in healthy subjects, however, its role is controversial in patients with chronic heart failure (CHF). The aim of this study was to clarify whether the oxygen transport capacity is an actual determinant of exercise capacity in CHF patients. Thirteen CHF patients underwent two maximum exercise tests, i.e., a graded protocol test and a fixed protocol test, measuring expiratory gases, leg blood flow (LBF), and arterial and venous blood gases. The workload of the fixed protocol was set to exceed the peak workload obtained by the graded protocol. Exercise with the fixed protocol caused significantly larger peak V(O2) compared to the graded protocol (813+/-194 to 971+/-203 ml/min, P<0.001). Peak LBF increased by 17%, while the peak leg arterio-venous oxygen difference increased by 5% from the graded protocol to the fixed protocol. The linear correlation between leg venous partial oxygen pressure and peak V(O2) was more clearly manifested in the fixed protocol (r=0.60, P<0.05) than in the graded protocol (r=0.47, NS). In conclusion, the exercise with graded protocol did not always conduct the upper limit of oxygen demand/supply relationship in CHF patients, whereas, the fixed protocol with a larger workload produced larger peak V(O2) and manifested the mechanism to limit V(O2) by oxygen transport capacity.