OBJECTIVE To analyze heart rate control in hospital emergency departments and outcomes in patients with recent onset atrial fibrillation (AF) so that targets for improvement can be identified. METHODS Multicenter, prospective observational cross-sectional study in a representative sample of 124 hospitals of the Spanish health services, based on records in the HERMES-AF database (Hospital Emergency Department Management Strategies for AF) for May 23 to June 5, 2011. Patients with symptomatic AF within 48 hours of onset were enrolled when the decision was made to attempt restoration of sinus rhythm. RESULTS We included 337 patients. Chemical cardioversion was used in 311 (92.3%) and electrical cardioversion in 52 (15%), after drugs had failed in half the cases. Sinus rhythm was restored in 278 patients (82.5%), and symptoms resolved in 94%. Adverse effects were recorded in 0.9% but none were serious. Amiodarone was independently associated with a lower rate of restored sinus rhythm (odds ratio [OR], 0.442; 95% CI, 0.238-0.823; P=.01) than electrical cardioversion (OR, 4.0; 95% CI, 1.2-13.3; P=.024). The use of class Ic antiarrhythmic agents was associated with a higher percentage of discharges in less than 6 hours (OR, 2.6; 95% CI, 1.6-4.3; P< .001), and amiodarone was associated with hospital stays longer than 24 hours (OR, 2.7; 95% CI, 1.5-4.8; P< .003). CONCLUSIONS Emergency department restoration of sinus rhythm in patients with AF is safe, effective, and associated with clinical benefits. Quality of care could be improved by replacing the use of amiodarone with faster and more effective treatments such as electrical cardioversion or the use of class Ic agents.