Aims: Predicting survival from peak exercise oxygen uptake(peak VO2) in chronic heart failure(CHF) is hindered by its reduction if exercise duration is submaximal. The oxygen uptake efficiency slope(OUES) is a non-linear description of the ventilatory response to exercise, which has the potential to describe abnormalities even early in exercise. We evaluated the physiology of OUES and assessed its potential for prognostic information in patients with CHF. Methods and results: Two hundred and forty-three patients with CHF(mean age 59± 12 years) underwent cardiopulmonary exercise testing between May 1992 and July 1996. Mean peak VO2 was 16.2± 6.7 mL/kg/min, VE/VCO2 slope 38± 12.5, ventilatory anaerobic threshold 10.9± 3.5 mL/kg/min, and OUES 1.6± 0.7 L/min. The value for each variable fell across the New York Heart Association classes(P< 0.0001 by analysis of variance for each). When only the first 50% of each exercise test was used to calculate the variables, the value obtained for OUES changed the least(peak VO2 25% difference and OUES 1% difference). After a median of 9 years of follow-up, 139 patients(57% ) had died. Each of the exercise variables was a significant univariate predictor of prognosis but in a multivariable model, only OUES was identified as the sole significant independent prognostic variable. Conclusion: OUES provides an effective, independent measure of pathological exercise physiology. Its numerical value is relatively insensitive to the duration of exercise data from which it is calculated. Its prognostic value seems to be stronger than the best available existing measures of exercise physiology. Aims: Predicting survival from peak exercise oxygen uptake (peak VO2) in chronic heart failure (CHF) is hindered by its reduction if exercise duration is submaximal. The oxygen uptake efficiency slope (OUES) is a non-linear description of the ventilatory response to exercise, which has the potential to describe abnormalities even early in exercise. We evaluated the physiology of OUES and assessed its potential for prognostic information in patients with CHF. Methods and results: Two hundred and forty-three patients with CHF (mean age 59 ± 12 years) underwent cardiopulmonary exercise testing between May 1992 and July 1996. Mean peak VO2 was 16.2 ± 6.7 mL / kg / min, VE / VCO2 slope 38 ± 12.5, ventilatory anaerobic threshold 10.9 ± 3.5 mL / kg / min, and OUES 1.6 ± 0.7 L / min. The value for each variable fell across the New York Heart Association classes (P <0.0001 by analysis of variance for each). When only the first 50% of each exercise test was used to calculate the variables, the value got for After a median of 9 years of follow-up, 139 patients (57%) had died. Each of the exercise variables was a significant univariate predictor of prognosis but (peak VO2 25% difference and OUES 1% difference) in a multivariable model, only OUES was identified as the sole significant independent prognostic variable. Conclusion: OUES provides an effective, independent measure of pathological exercise physiology. Its numerical value is relatively insensitive to the duration of exercise data from which it is calculated. prognostic value seems to be stronger than the best available existing measures of exercise physiology.