Background: Heart failure with midrange ejection fraction (HFmrEF) represents a heterogeneous category where phenotype, as well as prognostic assessment, remains debated. The present study explores a specific HFmrEF subset, namely those who recovered from a reduced EF (rec-HFmrEF) and, particularly, it focuses on the possible additive prognostic role of cardiopulmonary exercise testing. Methods and Results: We analyzed data from 4535 patients with HFrEF and 1176 patients with rec-HFmrEF from the Metabolic Exercise combined with Cardiac and Kidney Indexes database. The end point was cardiovascular death at 5 years. The median follow-up was 1343 days (25th–75th range 627–2403 days). Cardiovascular death occurred in 552 HFrEF and 61 rec-HFmrEF patients. The multivariate analysis confirmed an independent role of the MECKI score's variables in HFrEF (C-index = 0.744) whereas, in the rec-HFmrEF group, only age and peak oxygen uptake (pVO2) remained associated to the end point (C-index = 0.745). A peak oxygen uptake of ≤55% of predicted and a ventilatory efficiency of ≥31 resulted as the most accurate cut-off values in the outcome prediction. Conclusions: Present data support the cardiopulmonary exercise test and, particularly, the peak oxygen uptake, as a useful tool in the rec-HFmrEF prognostic assessment. A peak VO2 of ≤55% predicted and ventilatory efficiency of ≥31 might help to identify a high-risk rec-HFmrEF subgroup.