A 59-year-old man presents to the emergency department 45 minutes after onset of central chest pressure radiating to the left arm. He is diaphoretic and anxious. Blood pressure is 142/84 mm Hg, heart rate 96 beats/min, oxygen saturation 96% on room air. The initial ECG shows 2 mm ST depression in leads V4-V6 and T-wave inversion in leads II, III, and aVF. There is no contraindication to antiplatelet therapy. What is the single most appropriate immediate pharmacologic intervention?