BACKGROUND : Patients having heart failure with midrange ejection fraction (HFmrEF: 40% ≤ EF < 50%) are increasingly being considered a new subset of the population with heart failure. Despite recent advances in heart-failure treatment strategies, the prognosis of these patients has not improved substantially over time. In addition, the significance of this new phenotype in hospitalized patients with acute decompensated heart failure (ADHF), another population whose prognosis has not improved, also remains poorly understood. This study aimed to describe the clinical characteristics, prognosis and treatment responses of patients with HFmrEF hospitalized for ADHF. METHODS : On the basis of consecutive inpatient data from a multicenter ADHF registry, 651 of 3572 patients (17.1%) were classified as having HFmrEF. Prognostic factors predicting composite outcomes, defined as all-cause death and heart failure readmission, as well as all-cause death alone, were analyzed. RESULTS : In the median follow-up duration of 724 days, both composite endpoints and all-cause death alone were comparable in those with heart failure with preserved ejection fraction, HFmrEF and heart failure with reduced ejection fraction. Age, anemia, hyponatremia, elevated blood urea nitrogen, chronic kidney disease, and elevated plasma brain natriuretic peptide levels were significant predictors of composite outcomes in HFmrEF. CONCLUSIONS : Roughly one-sixth of the patients with ADHF had HFmrEF. The long-term prognosis of patients with HFmrEF was not significantly different from that of patients with heart failure with preserved ejection fraction and heart failure with reduced ejection fraction in the population with ADHF. Risk factors for adverse outcomes in HFmrEF were also similar to those for heart failure with preserved ejection fraction and HFmrEF in the hospitalized population with ADHF.