A man in his 30s with no history of cardiovascular disease presented to the emergency department with exertional chest distress. On admission the patient’s blood pressure was 132/88 mm Hg; respiratory rate, 18 breaths per minute; and pulse, 88 beats per minute. Cardiopulmonary examination findings were unremarkable. The result of high-sensitivity cardiac troponin level testing was 0.148 ng/mL (reference range, <0.02 ng/mL; to convert to μg/L, multiply by 1.0). A 12-lead electrocardiogram (ECG) was obtained on admission (Figure).