The 9-minute self-powered treadmill (SPT) test has been employed to evaluate submaximal exercise tolerance in CHF, but its relationship to maximum exercise capacity is not well defined. Therefore, we examined the relationship of the distance walked during 9 minutes on a SPT to indices of respiratory gas exchange on the SPT and on a maximal treadmill test (modified Naughton protocol). 10 patients (PTS) with NYHA class II–III CHF (EF 20 ± 2%), and 6 age-matched sedentary controls (CON) were studied. CHF PTS walked less far (386 ± 38 vs 643 ± 21 m, p < 0.001) and stopped more often (27 stops in 9 PTS vs no stops in CON, p < 0.05). The highest VO 2 achieved on the SPT (SPT-VO 2 ) and the peak VO 2 on the maximal treadmill (peak VO 2 ) were both lower in CHF PTS (15.9 ± 1.4 vs 251 ± 0.9 and 16.5 ± 1.5 vs 309 ± 3.1 ml/kg/min respectively, both p < 0.001). SPT distance correlated poorly with EF (r = 0.331 and insignificantly with NYHA class (r = -0.47, P = 0.13), but very closely with both SPT-VO 2 and peak-VO 2 (r = 0.8 = and r = 0.89, respectively, both p < 0.005). SPT-VO 2 correlated closely with peak-VO 2 (r = 0.79, P = 0.006) in CHF PTS but not significantly in CON. Of note is that all CHF PTS achieved anaerobic threshold on the SPT vs only 1/6 CON (p < 0.05). and SPT-VO 2 was 97.3% of the treadmill peak-VO 2 vs 83.8% in the CON. These findings demonstrate that in motivated subjects with moderate CHF, in distinction to control subjects, the 9-minute SPT test is more an index of maximal than submaximal exercise capacity. Although it may be useful in assessing exercise tolerance, this may explain why SPT, like other measurements of maximal exercise capacity, does not correlate well with symptom status in these patients.