A man in his 60s presented with dull, right-sided shoulder pain of 12 hours’ duration relieved by nitroglycerin. He reported escalating exertional chest discomfort with dyspnea over the preceding weeks. Medical history included a provoked deep vein thrombosis and chronic obstructive pulmonary disease. He took no new medications or supplements, and had not travelled significantly. Examination revealed an S4 heart sound at the apex and bilateral lower extremity edema. His high-sensitivity troponin-T level was 1365 ng/L at presentation and 1310 ng/L at 6 hours (normal range, 0-14 ng/L). Laboratory investigations were remarkable for an eosinophil level of 78 000/μL (reference range, 0-7000 μL). His initial electrocardiogram (ECG) is shown in Figure 1. (To convert eosinophils to 109/L, multiply by 0.001.)