A 22-year-old Hispanic man presented to the emergency department with palpitation after playing basketball. He had similar episodes of palpitation associated with exercise, which disappeared spontaneously. He denied any previous cardiac history. On examination, he appeared diaphoretic with a blood pressure of 96/60 mm Hg. His heart rate was above 200 beats/min. His lungs were clear to percussion and auscultation. The rest of his examination findings were normal. His complete blood cell count and serum electrolyte, creatinine, glucose, and troponin-I levels were normal. The presenting electrocardiogram (ECG) is shown in Figure 1.