A 58-year-old man presents to the emergency department with 45 minutes of central crushing chest pain radiating to his left arm. His ECG shows ST elevation in leads V2–V5. He is alert, has no history of major bleeding, and is not taking anticoagulants. Observations: BP 138/82 mmHg, HR 96 bpm, SpO2 97% on air. No treatment has yet been given. What is the single most appropriate immediate medication to administer?