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Atrial flutter with flecainide-induced 1:1 conduction at a rate <200 b.p.m. at rest: a case report. Background : Class IC antiarrhythmic drug flecainide is commonly used in the management of atrial arrhythmias and in particular atrial fibrillation (AF). Although previously reported as a potential complication, atrial flutter (AFL) with 1:1 atrioventricular (AV) conduction is rare, with only few cases reported so far, most of which related to physical activity. In all previous reported cases, 1:1 conduction resulted in ventricular rates of >200 b.p.m. Case summary : We report the case of a 60-year-old woman, who presented to our local emergency department with palpitations related to acute onset AF. The patient developed symptomatic 1:1 AFL with a rate of 192 b.p.m., shortly after administration of intravenous flecainide, which spontaneously converted back to AF and subsequently to sinus rhythm, with further administration of amiodarone and beta-blocker. Discussion : The case raises awareness of this rare but potentially life-threatening complication to those using flecainide for pharmacological cardioversion of AF. QRS complex widening can be seen in the context of very rapid ventricular rates, posing additional diagnostic challenge, especially with rates of <200 b.p.m. Prescribing an AV nodal blocking agent, such as a beta-blocker, together with flecainide reduces significantly the risk of 1:1 conduction and should always be considered.