The 2021 CAEP Acute Atrial Fibrillation/Flutter Best Practices Checklist has been updated from the original version published in 2018.1 These checklists have been created to assist emergency physicians in Canada and elsewhere manage patients who present to the emergency department (ED) with acute/recent-onset atrial fibrillation (AF) or flutter (AFL). The checklist focuses on symptomatic patients with acute AF or AFL, i.e. those with recent-onset episodes (either first detected, recurrent paroxysmal or recurrent persistent episodes) where the onset is generally less than 48 hours but may be as much as seven days. These are the most common acute arrhythmia cases requiring care in the ED. Canadian emergency physicians are known for publishing widely on this topic and for managing these patients quickly and efficiently in the ED. 2 3 4