The prevalence of heart failure considerably increased over the last three decades because of the aging population and the improved survival rate after acute cardiac events.1,2 Clinical and research programs more frequently are directed to patients with severely impaired functional capacity. Nevertheless, heart failure with mid-range left ventricular dysfunction (HFmrEF) has been recently defined as a distinct clinical entity.3 Cardiorespiratory fitness (CRF), usually best reflected by peak oxygen consumption (VO2peak), has been shown to be a powerful and independent prognostic marker in patients with heart failure.4–10 CRF has been linked to both cardiovascular and non-cardiovascular outcomes in ambulatory patients with heart failure.1 VO2peak is strongly related to walking capacity in older adults,11 and among heart failure patients.12 The walking speed maintained during a submaximal 1-km treadmill walk (1 k-TWT) has been demonstrated to be a valid and simple tool for VO2peak estimation,12–14 and is inversely related to survival,15–17 and hospitalization, 18 in outpatients with cardiovascular disease and preserved left ventricular ejection fraction (LVEF). We examine the association between VO2peak estimated by the 1 k-TWT and all-cause mortality in men with HFmrEF. We studied 209 medically stable male outpatients aged 6510 years, with LVEF 40%5%, referred to our exercise-based secondary prevention program. Each patient performed the moderate perceptually- regulated (11–13 on the 6–20 Borg scale) 1 k-TWT. Time to walk 1-km, mean and maximal heart rates during the walk, age, height, and weight were entered into the equations for VO2 peak estimation.13 Based on the VO2peak, the sample was subdivided into tertiles and mortality risks were calculated during a median follow up of 9.4 years. The local Ethics Committee approved the study protocol, and all patients gave written informed consent. Survival decreased in a graded fashion from the highest VO2peak tertile to the lowest tertile (p<0.0001, Figure 1). During the follow-up period, 23, 11, and 3 all-cause deaths occurred among the lowest, intermediate, and highest VO2peak tertile respectively. Mortality rate was independent from traditional cardiovascular risk factors, including LVEF and clinical history. Compared with the lowest tertile (mean walking speed 2.8 km/h), the full-adjusted mortality risk decreased for the second (mean walking speed 3.8 km/h), and third tertile (mean walking speed 4.6 km/h), with hazard ratios of 0.64 (95% confidence interval (CI): 0.33–1.20, p¼0.18), and 0.26 (95% CI: 0.08–0.80, p¼0.02), respectively (p for trend<0.0001). These results are similar to those obtained by other studies in which VO2peak was determined by maximal cardiopulmonary exercise testing.19–21 Consistent with previous studies,1 we observed a 24.5% reduction in all cause mortality associated with each 1-Metabolic equivalent (MET) increment in VO2peak (p¼0.04). In conclusion, our findings show that VO2peak estimortality among men with HFmrEF. These results may have practical implications in the context of transitioning from clinically based and supervised training programs to fitness facilities or self-guided exercise programs.