A man in his 20s presented to the emergency department with 1 day of chest pressure. He reported no medical history. Four days prior to presentation he had experienced subjective fevers, rhinorrhea, a dry cough, and sinus congestion. The day prior to presentation he had experienced 3 hours of substernal pressure that resolved spontaneously. In the early morning of the day of presentation, he was awakened from sleep by constant chest pressure radiating to the right jaw, diaphoresis, and 1 episode of vomiting. Vital signs obtained in the Emergency Department were within normal limits. Cardiac examination revealed a regular rate and rhythm, normal point of maximum impulse without lifts, and no murmurs, rubs, or gallops in supine, sitting, or standing positions. The remainder of the physical examination was within normal limits. The initial electrocardiogram (ECG) is shown in the Figure. The initial serum troponin I level was 6.18 ng/mL (to convert to micrograms per liter, multiply by 1.0).