AimsTo investigate whether the presence of atrial fibrillation (AF) is independently associated with adverse short-term outcomes in patients diagnosed with acute heart failure (AHF) in the emergency department (ED).MethodsWe performed a secondary analysis of patients included in the EAHFE registries 4&5. Patients were divided by the presence of sinus rhythm (SR) or AF at ED arrival. The primary outcome was 30-day all-cause mortality. Secondary outcomes included the 30-day post-discharge combined endpoint of ED revisit or hospitalisation due to AHF and all-cause mortality. We recorded 54 independent variables that can affect outcomes. Cox regression was used to investigate adjusted significant associations between AF and outcomes. Analyses were repeated according to whether AF was previously known and whether AF was considered responsible for the AHF episode.ResultsWe analysed 6045 ED visits (mean age 80.4 years, 55.9% women), 3644 (60.3%) with AF. The cumulative 30-day mortality was 9.4%, and the adverse combined endpoint (ACE) was 25.9% (ED revisit with and without hospitalisation were 16.5 and 8.9% and death occurred in 4.7%). No differences were found in outcomes of AHF patients with SR and AF, and among the latter group, no differences were found depending on whether AF was considered responsible for the AHF episode. Patients with previously known AF had significantly lower 30-day mortality and higher post-discharge ACE rates, although these differences disappeared after adjustment for confounders HR 0.782, 95% CI 0.590–1.037, p = 0.087; and HR 1.131, 95% CI 0.924–1.385, p = 0.234).ConclusionThe coexistence of AF does not impact the short-term outcomes of patients diagnosed with AHF in the ED.