Introduction The first aim of this study was to investigate the characteristics for elderly patients with acute heart failure presenting to the emergency department (ED). The second aim was to determine the characteristics of these elderly patients associated with serious adverse events. Methods The population was divided into 2 age groups, <80 and ≥80 years. The primary outcome was the occurrence of a serious adverse event, defined as either death from any cause within 30 days of the index ED visit or any of the following events within 14 days of the index ED visit: admission to a monitored unit, intubation, need for noninvasive ventilation, myocardial infarction, major procedure, or, for patients who were discharged after the initial visit, return to the ED resulting in admission to hospital. Results This prospective cohort study included 1658 visits. Older patients had a lower heart rate and higher diastolic blood pressure. The older patients were more likely to experience hospital admission (56% vs 46%, P < .001). For patients 80 years or older, 109 (14%) experienced a serious adverse event. In this ≥80-year group, history of heart failure, current medication with antiarrhythmic, acute infarction on the arrival electrocardiography, chest x-ray with pleural effusion, and urea greater than 12 mmol/L were independently associated with short-term serious adverse events. Conclusions Elderly patients with heart failure are a high-risk group. Careful assessment of these factors could help physicians identify those patients most at risk for adverse outcomes and, therefore, most in need of hospital admission.