Abstract Objectives. This study sought to 1) assess the short-, medium- and long-term prognostic power of peak oxygen consumption (V̇ o 2) in patients with heart failure; 2) verify the consistency of a nonmeasurable anaerobic threshold (AT) as a criterion of nonapplicability of peak V̇ o 2; 3) develop simple rules for the efficient use of peak V̇ o 2 in individualized prognostic stratification and clinical decision making. Background. Peak V̇ o 2, when AT is identified, is among the indicators for heart transplant eligibility. However, in clinical practice the application of defined peak V̇ o 2 cutoff values to all patients could be inappropriate and misleading. Methods. Six hundred fifty-three patients consecutively considered for eligibility for heart transplantation were followed up. Outcomes (cardiac death and urgent transplantation) were determined when all survivors had a minimum of 6 months of follow-up. Results. Contraindication to the exercise test identified very high risk patients. The relatively small sample of women did not allow inferences to be drawn. In men, peak V̇ o 2 stratified into three levels (≤10, 10 to 18 and >18 ml/kg per min) identified groups at high, medium and low risk, respectively. The prognostic power of peak V̇ o 2 ≤10 ml/kg per min was maintained even when the AT was not detected. In patients in New York Heart Association functional class III or IV, peak V̇ o 2 did not have prognostic power. In patients in functional class I or II, peak V̇ o 2 stratification was prognostically valuable, but less so at 6 than at 12 or 24 months. Age did not influence peak V̇ o 2 prognostic stratification. Conclusions. A contraindication to exercise testing should be considered a priority for listing patients for heart transplantation. Only in less symptomatic male patients does a peak V̇ o 2 ≤10 ml/kg per min identify short-, medium- and long-term high risk groups. A peak V̇ o 2 >18 ml/kg per min implies good prognosis with medical therapy.