A 45-year-old man presents to the emergency department after a syncopal episode while walking his dog. He reports a six-week history of intermittent lightheadedness and palpitations, particularly with exertion. He denies chest pain, dyspnea, or fever. His past medical history is notable for a persistent dry cough a year ago that resolved spontaneously without treatment. He takes no regular medications and has no known allergies. He is a non-smoker and consumes alcohol socially. The family history is noncontributory for premature cardiac disease or sudden death.