Background: The clinical characteristics and outcomes of acute heart failure (AHF) according to left ventricular ejection fraction (LVEF) have not been fully elucidated, especially for patients with mid-range LVEF. We performed a comprehensive comparison of the epidemiology, patterns of in-hospital management, and clinical outcomes in AHF patients with different LVEF categories. Methods and Results: The Korean Acute Heart Failure (KorAHF) registry is a prospective multicenter cohort of hospitalized AHF patients in Korea. A total of 5,374 patients enrolled in the KorAHF registry were classified according to LVEF based on the 2016 ESC guidelines. More than half of the HF patients (58%) had reduced EF (HFrEF), 16% had mid-range EF (HFmrEF), and 25% had preserved EF (HFpEF). The HFmrEF patients showed intermediate epidemiological profiles between HFrEF and HFpEF and had a propensity to present as de-novo HF with ischemic etiology. Patients with lower LVEF had worse short-term outcomes, and the all-cause in-hospital mortality, including urgent heart transplantation, of HFrEF, HFmrEF, and HFpEF was 7.1%, 3.6%, and 3.0%, respectively. Overall, discharged AHF patients showed poor 3-year all-cause death up to 38%, which was comparable between LVEF subgroups (P=0.623). Conclusions: Each LVEF subgroup of AHF patients was a heterogeneous population with diverse characteristics, which have a significant effect on the clinical outcomes. This finding suggested that focused phenotyping of AHF patients could help identify the optimal management strategy and develop novel effective therapies.