Abstract Objective To determine whether the presence of a short-stay unit(SSU) in a hospital influences the percentage of admissions, length of hospital stay(LOS) and outcomes in emergency department(ED) patients with acute heart failure(AHF). Method Retrospective analysis of AHF patients presenting to one of 34 Spanish ED included in EAHFE registry. Baseline and ED data of patients were collected. Patients were classified into two groups in function of being attended at hospitals with or without a SSU. Main outcome variables were the percentage of admissions from ED, and LOS for admitted patients. Secondary variables were all-cause death and ED revisits for worsening heart failure within 30 days following discharge. Results Of 9078 patients presenting to the ED (SSU 5191; no SSU 3887), 6796 (74.8%) were admitted. Compared to hospitals without a SSU, the admission rate in hospitals with a SSU was 8.9% higher (95%CI 6.5%–11.4%), but 30-day ED revisit and mortality rates were lower among patients discharged directly from the ED (− 10.3%, 95%CI − 16,9% to − 3.7%; and − 10.0%, 95%CI − 16.6 to − 3.4%, respectively). For admitted patients, the overall LOS was 9.3 ± 9.5 days, being 2.2 days shorter (95%CI − 2.7 to − 1.7) in hospitals with a SSU, with no significant differences in in-hospital, 30-day mortality or 30-day ED revisit rates. Conclusions The data suggest that SSU may improve the safety of emergency care of patients with AHF, but at the cost of a higher rate of hospital admissions, and it may also reduce the LOS for admitted patients without affecting post discharge safety.