Introduction: The Canadian Association of Emergency Physicians (CAEP) Atrial Fibrillation (AF) Guidelines prioritizes early cardioversion and discharge home in the management of rapid AF, however not all patients can be safely cardioverted in the emergency department (ED). Given limited ED-based evidence on rate control, we sought to better understand the burden of disease in AF patients not managed by rhythm control and identify opportunities for improved care. Methods: We conducted a health records review of consecutive AF patient visits at two Canadian academic hospital EDs over a 12-month period. We included all patients ≥18 years with AF on electrocardiogram, a heart rate ≥100 beats per minute (bpm), and who did not receive cardioversion. Outcomes included: (1) incidence of patients managed by rate control; (2) specific rate control management practices including choice of agent, route of administration, dosing, and timing; (3) adverse events; (4) compliance with CAEP AF Guidelines; and (5) disposition and outcomes. Results: Of 972 rapid AF patient visits, 307 were excluded and 665 were included, with mean age 77.2, female 51.6%. Of those included, 43.0% were given rate control medications, most common being metoprolol (72.0%). Admission to hospital occurred in 61.4% of visits, and 77.9% of AF cases were secondary to another medical condition. In those given rate control medications, 9.1% suffered adverse events and only 55.6% had a final ED heart rate ≤100 bpm. Inappropriate use of rate control medications was found in 44.8% of cases, specifically inappropriate choice of agent (4.5%), inappropriate route of administration (26.9%), over-dosed (2.4%), under-dosed (5.2%), and inadequate timing (5.6%). Conclusion: We demonstrated that for rapid AF patients not receiving cardioversion, most cases were secondary to a medical cause and of those receiving rate control, there were a concerning number of adverse events related to inappropriate choice of agent, route of administration, dosage, and timing. Moving forward, better awareness of the CAEP AF Guidelines by ED physicians will ensure safer use of rate control agents for rapid AF patients.