Stable angina

A 56-year-old man comes to the emergency department because of chest pain and pressure he experienced an hour ago while shoveling snow. He has had recurrent bouts of this pain over the past year, and he says that it usually radiates to his jaw and left arm, and goes away when he sits down to rest. Today's episode lasted five minutes, he has come to the ED at the urging of his family. He has a 10-year history of hyperlipidemia and type 2 diabetes mellitus. Current medications include atorvastatin and metformin. His temperature is 37.1°C (98.8°F), pulse is 87/min, respirations are 19/min, and blood pressure is 130/85 mm Hg. Initial laboratory studies show a troponin I level of less than 0.01 ng/mL. Chest X-ray and ECG show no abnormalities. Which of the following is the most likely diagnosis?