Purpose: Although V̇O2 max is considered the gold standard measure of cardiorespiratory fitness (CRF), it can be difficult to attain in patients with cardiovascular disease (CVD). The submaximal oxygen uptake efficiency slope (OUES) integrates cardiovascular, musculoskeletal and respiratory function during incremental exercise into a single index and has been proposed as an alternative and effort independent measure of cardiopulmonary reserve (Baba et al., 1996). The purpose of this study was to examine the relation between V̇O2 max and both submaximal absolute OUES and relative OUES (OUES.kg-1). Methods: A total of 55 men ((mean ± SD) age, 59.08 ± 9.03 yr; VO2 max, 1.94 ± 0.53 L.min-1and 22.73 ± 5.95 mL.kg-1.min-1) were recruited during induction to a community based exercise referral program following completion of phase 2 cardiac rehabilitation. Participants performed a graded exercise test on a cycle ergometer with breath-by-breath open circuit spirometry and a 12 lead ECG. Absolute OUES and OUES.kg-1 were calculated by plotting VO2 in mL.min-1 on the x-axis, and the log transformed VE on the y-axis (VO2 = a log 10 VE + b). Exercise data up to the ventilatory anaerobic threshold (VAT) was included in the analysis. Results: The %V̇O2 max corresponding to the VAT was 55.72 ± 11.81. Absolute OUES and OUES.kg-1 were 2164.42 ± 540.96 and 25.28 ± 5.99, respectively. There was a significant positive correlation between V̇O2 max (L.min-1) and OUES (r= 0.775; p<0.001) and between V̇O2 max (mL.kg-1.min-1) and OUES.kg-1 (r= 0.78; p<0.001). Conclusion: Determination of V̇O2 max is not often feasible in individuals with CVD where maximal exercise testing is contraindicated or when performance may be impaired by pain, dyspnea or angina. The findings from the present study indicate that the OUES and OUES.kg-1 are significantly related to absolute and relative V̇O2 max, respectively and may be used as a valid sub maximal effort independent measure of CRF.