A patient in their 60s presented to the emergency department because of retrosternal chest pain for the past 5 hours. The patient was known to have diabetes and hypertension and a 40-pack-year smoking history. The patient had similar episodes of chest pain in the past, which were aggravated with exertion and relieved with resting. At presentation, blood pressure was 141/90 mm Hg; pulse, 89 beats/min; respiratory rate, 22 breaths/min; and oxygen saturation, 99% on room air. The electrocardiogram (ECG) obtained at presentation is shown in the Figure, A. Loading doses of aspirin and clopidogrel were administered along with sublingual nitroglycerin, after which the patient reported partial relief of chest pain, and a second ECG was obtained. High-sensitivity cardiac troponin assay was performed and returned negative (<0.05 ng/mL; to convert to μg/L, multiply by 1.0). However, the patient’s chest pain recurred after a half hour, during which another ECG was obtained, which is shown in the Figure, B.