Illustration of an electrocardiogram (ECG) from a 47 year old admitted to hospital when he did not pay attention to intermittent chest pain for 2 days. High-sensitivity troponin is positive. Coronary angiography revealed 99% subtotal occlusion of the middle of left anterior descending branch. The clinical diagnosis is acute myocardial infarction, but his electrocardiogram changes are not typical, and acute myocardial infarction cannot be directly diagnosed.