A patient with a history of myocardial infarction becomes dizzy and light-headed shortly after receiving local anesthesia. What should be your first action?

Dizziness following local anesthetic administration in a patient with cardiac history requires immediate assessment. The first action is to stop the procedure, assess the patient (check vital signs and responsiveness), and administer supplemental oxygen (100% O2 via face mask). Oxygen supports myocardial perfusion and addresses any hypoxia. In this context, dizziness is most commonly due to vasovagal syncope or orthostatic hypotension. If syncope is confirmed, the patient should be placed in the supine position with legs elevated (Trendelenburg). If acute MI is suspected, summon EMS and administer aspirin. Oxygen first is the correct initial step in this undifferentiated scenario.