A man in his 40s with a long-term smoking history was referred to the emergency department with persistent chest pain accompanied by sweating and nausea, which had been present for a half-hour. On admission, the patient’s vital signs were as follows: blood pressure of 116/74 mm Hg, a regular pulse of 86 beats/min, and a respiratory rate of 19 breaths/min. Cardiopulmonary examination showed no remarkable findings. The initial troponin I level was less than 0.03 ng/mL (normal range, <0.03 ng/mL; to convert to μg/L, multiply by 1.0). An initial 12-lead electrocardiogram (ECG) was performed immediately on admission (Figure, A). Approximately 1 hour later, a preoperative ECG was performed (Figure, B).