A patient in their 70s presented to the emergency department with acute chest pain that had lasted 3 hours. The patient had no history of chronic disease or acute infection and denied any tobacco, alcohol, or illicit drug use. During a routine physical examination 1 month prior, no abnormality was found on the patient’s electrocardiogram (ECG). At admission, blood pressure and pulse rate were 157/93 mm Hg and 63 beats/min, respectively. The troponin I level was 0.1394 ng/mL (normal range: 0-0.0342 ng/mL; to convert to μg/L, multiply by 1.0), and brain-type natriuretic peptide level was 213.60 pg/mL (normal range: 0-100 pg/mL; to convert to ng/L, multiply by 1.0). The admission ECG was obtained at our hospital (Figure, A). A repeated ECG was obtained after 1 hour (Figure, B).