Introduction: Patients with atrial fibrillation (AF) of <48 hours duration often present to Emergency Departments (ED). Electrical or chemical cardioversion can be employed to restore normal sinus rhythm (NSR). Current guidelines make no recommendations between these two methods and the management decisions are left to the discretion of the treating physician. The objective of this study was to compare these two approaches in terms of ED length of stay (LOS), success (conversion to NSR) and health related outcomes. Methods: At six western Canadian EDs, eligible adult patients were assigned to one of two groups following concealed allocation and using a centralized computer-generated randomization method: electrical cardioversion (EC) first (followed by chemical cardioversion [CC] if the primary method failed) or CC first (followed by EC if the primary method failed). Baseline evaluation/interview and 3/30 day telephone contact were completed and documented using the REDCap data-platform. Adverse events were externally adjudicated in a blinded-fashion. An intention to treat analysis was performed. Results: Overall, 84 patients participated in the study (EC: 43; CC: 41); the median age was 60 years (interquartile range [IQR]: 50, 66), and 38% were female. The baseline patient characteristics in both groups were similar. The median LOS between randomization and conversion to NSR (intervention LOS) was 1.0 hrs (IQR: 0.8, 2.7) in EC vs. 3.1 hrs (IQR: 2.0, 3.9) in CC (p<0.001); more patients in EC were discharged from the ED within 4 hours than in the CC group (65% vs. 32%; p=0.002). The majority of EC patients (84%) converted to NSR after the first attempt while half of the patients did so in the CC group (49%). No differences were observed in terms of adverse events (26% vs. 24%; mostly minimal), hospitalizations (0%), and patients’ health outcomes (physician/ED visits, admissions, stroke) and status (SF-8) at 3 and 30 days, in groups EC and CC groups, respectively. Conclusion: Electrical cardioversion was associated with a statistically significant and clinically meaningful reduction in the LOS when compared to cardioversion using chemical management. Similarities in the proportions of success, adverse events and health outcomes between the groups would support the use of electrical shock as the first approach for cardioversion in clinical practice.