BACKGROUND:Atrial fibrillation (AF) is the most common arrhythmia treated in the emergency department (ED), with primary electrical cardioversion (PEC) the preferred method of rhythm control. Anecdotally, patients undergoing ED procedural sedation (EDPS) for PEC differ from those requiring EDPS for other procedures:they are at higher risk of adverse events, and require fewer drugs and lower doses. We attempt to verify this using an EDPS registry at a Canadian, tertiary care teaching hospital. METHODS:This is a retrospective review of patients that underwent EDPS for the period of June 2006 to September 2014. We compared demographics, medication use and intra-procedural adverse events between those receiving EDPS for PEC for AF compared to that for other indications. We report the asssociation between AEs and predictors using logistic regression. RESULTS:A total of 4867 patients were included, 714 for PEC for AF and 4153 for other indications. PEC patients were more likely male (58.5％vs. 47.1％), older (59.5 years vs. 48.1 years), and less likely to be ASA I (46.6％ vs. 69.0％). PEC patients received smaller doses of propofol and less likely to receive adjuvant analgesic therapy (11.5％ vs. 78.2％). PEC patients were more likely to experience hypotension (27.6％vs. 16.5％) but respiratory AEs (apnea, hypoxia and airway intervention) were not different. CONCLUSION:EDPS for PEC differs from that conducted for other purposes:patients tend to be less healthy, receive smaller doses of medication and more likely to suffer hypotension without an increase in respiratory AEs. These factors should be considered when performing EDPS.