Andersen-Tawil syndrome is a rare autosomal dominant genetic or sporadic disorder characterized by periodic paralysis, ventricular arrhythmias and dysmorphic features. Ventricular arrhythmias can include frequent premature ventricular complex, polymorphic ventricular tachycardia, and less frequently bidirectional ventricular tachycardia. Left ventricle function has been reported in only a few individual cases of Andersen-Tawil syndrome. A 14-year-old female patient was referred to our clinic from another center with documented arrhythmia and left ventricular systolic dysfunction. Andersen-Tawil syndrome was suspected and the diagnosis was confirmed after detection of a previously unreported mutation in children. We report the successful use of flecainide in bidirectional ventricular tachycardia and tachycardia-induced cardiomyopathy in a case of AndersenTawil syndrome associated with a novel mutation.