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Figure 3 Serial changes are depicted between the prehospital (left) and initial hospital (right) ECG in a patient with chest pain. The prehospital ECG shows subtle ST-T wave abnormalities that are nondiagnostic of myocardial ischemia. On the initial hospital ECG, obtained 36 min after the prehospital tracing, ST segment elevation is now evident in leads I, aVL and V₂, with ST segment depression and T wave inversion in the inferior leads (II, III and aVF).