A 45-yeаr-оld depаrtment stоre sаlesman has just cоmpleted a large lunch and complains of a dull substernal chest pain. You find the patient short of breath, apprehensive and perspiring profusely. His vitals are: BP 150/90, P 72 equal at the neck and wrist, R 22. From this history, which of the following is most likely?