Flecainide is recommended as a first-line antiarrhythmic drug to maintain normal 
sinus rhythm in patients with atrial fibrillation (AF) who have structurally 
normal hearts or hypertension without left ventricular hypertrophy. Flecainide 
is a sodium channel blocker with minimal effects expected on ventricular 
repolarization. We describe the case of a 32-year-old man with a structurally 
normal heart and persistent AF who was started on diltiazem and flecainide 50 mg 
twice/day approximately a year prior to presentation. Due to persistent and 
bothersome symptoms, his dose was increased to 150 mg twice/day, which was 
associated with a progressive lengthening of his corrected QT interval. On the 
day of presentation, he underwent an exercise test as part of his job 
requirements. While running, he felt lightheaded and experienced a syncopal 
event and cardiac arrest. An automated external defibrillator was available that 
displayed polymorphic ventricular tachycardia. The patient was successfully 
resuscitated. Although rare, this case suggests that flecainide can induce QT 
prolongation leading to torsades de pointes. Clinicians should be aware and 
consider periodic evaluations with electrocardiograms.