This study investigates the prognosis of acute decompensated heart failure (ADHF) on admission (i.e., primary ADHF) as compared to ADHF onset during course of hospitalization (i.e., secondary ADHF) in patients hospitalized with heart failure with mildly reduced ejection fraction (HFmrEF). Limited data regarding the prognostic impact of the timing of onset of ADHF is available. Consecutive patients with HFmrEF and ADHF were retrospectively included at one institution from 2016 to 2022. …