1472 The method for assessing exercise capacity in patients with congestive heart failure (CHF) remains controversial. PURPOSE: We critically assessed the O2 requirement of a submaximal fixed load exercise protocol tailored individually at the ventilatory threshold in patients with symptomatic CHF and compared it to healthy subjects. METHODS: The ventilatory parameters of thirty patients with symptomatic CHF caused by ischemic heart disease (n = 13), dilated cardiomyopathy (n = 11), or other causes (n = 6), mean age of 56 ± 12 years and mean LV ejection fraction 26 ± 7% were compared to those of 10 age-matched healthy volunteers. Maximal exercise capacity with gas exchange analysis was performed on a treadmill using a RAMP protocol. Submaximal exercise testing was performed using a constant workload slightly above the ventilatory threshold (VT). RESULTS: There was a delay in attainment of a VO2 steady state during the submaximal test in patients with CHF compared to healthy subjects. This was demonstrated by a delay in the time constant (TC), and delta between VO2 at baseline and at 3 minutes during submaximal testing. Also, the VT is reached at a lower percentage of the VO2 max in controls subjects (73% of VO2 peak) than in patients (79% of VO2 peak) (p = 0.0041). Moreover, during the submaximal test, VO2 reached at the 6th minute within the test and at maximal exhaustion was significantly higher than the VO2 predicted for each work rate (p< 0.05) for both patients and healthy subjects. CONCLUSION: Patients with CHF adapt differently when performing an endurance protocol slightly above the ventilatory threshold. This could be explained by the inability of these patients to reach true maximal oxygen consumption. The use of submaximal exercise testing as a functional measure in CHF is an appropriate alternative to maximal exercise testing.