1. A 55-year-old man presents to the emergency room with crushing substernal pain and left shoulder pain of 2 hours duration. The pain is not relieved by sublingual nitroglycerin, and the electrocardiogram shows ST elevation in several leads. Aspirin and streptokinase therapy are initiated, and the patient is admitted to the intensive care unit. The next morning, serum cardiac enzymes are elevated to 4 times the upper limit of normal, and the electrocardiographic changes are still present. Which of the following is the most likely diagnosis?