Introduction: Atrial fibrillation and flutter (AFF) represent the most common arrhythmia presentations to emergency departments (EDs). Some research suggests that women with AFF experience different symptoms, receive different treatment and have worse outcomes than men. This study explored sex differences in risk factors, medication, and outcomes before and after ED visits for acute AFF. Methods: Adult patients presenting to the one of three hospitals affiliated with the University of Alberta with acute AFF were enrolled. Following informed consent, each patient completed a survey administered by a trained researcher, administrative ED information (e.g., ED times) was collected from the ED information system, a chart review on treatments was conducted and patients were contacted for follow-up at 7 days via telephone. Descriptive (median and interquartile range {IQR} and proportions) and simple (Wilcoxon-Mann-Whitney, chi-square, z-proportion) statistics are presented for continuous and dichotomous outcomes. Results: Overall, 217 patients were enrolled; the median age was 64 years (IQR: 55, 73) and 39% were female. Males presenting to the ED with AFF were 10 years younger than females (p<0.001); however, females weighed significantly less (median weight 69 vs. 95 kg; p<0.001), consumed less alcohol (12 vs 60 drinks/year; p<0.001) and were less likely to be ex-smokers (p=0.022) than men with AFF. Women arrived by Emergency Medical Services (EMS) (p=0.037), experienced palpitations (p=0.042), and reported a history of hypertension (p=0.022) more frequently than men. Females were more often prescribed oral anticoagulants before (p= 0.041) and after (p=0.011) the ED visit, and females with a history of AFF were less likely to present without anticoagulant/antiplatelet therapy (p=0.015). Overall, both sexes had similar attempts at cardioversion (59.4% vs. 61.3%) and hospitalizations (12.5% vs. 8.6%), respectively. If initial chemical cardioversion failed, females were more likely to receive subsequent electrical cardioversion (60.0% vs. 26.7%, p=0.036) than men. Conclusion: Overall, both women and men present frequently to the ED with AFF. Compared to men with AFF, women present with symptoms 10 years later, have different risk factors, experience more severe symptoms and use EMS more commonly; however, outcomes were similar. Unexplained sex-based variations in-ED and post-ED management are evident and these differences warrant further scrutiny.