A 62-year-old man comes to the cardiology clinic because of chest discomfort that occurs when he walks uphill on his mail delivery route. He has noticed this sensation for the past 3 months. He describes the discomfort as a pressure or tightness across his chest that comes on predictably when walking uphill or carrying two heavy mail bags. The same activities consistently trigger the symptoms. The pressure lasts 2-3 minutes during the activity and goes away within 5 minutes after he sits down and rests. He has no symptoms when walking on level ground or when at rest, and he has never experienced these symptoms at night. Medical history includes hypertension and hyperlipidemia, both well-controlled on lisinopril and atorvastatin. He quit smoking 5 years ago after a 20-pack-year history. His temperature is 37.0°C (98.6°F), pulse is 72/min and regular, respirations are 14/min, and blood pressure is 138/84 mm Hg. Physical examination shows a well-appearing man in no acute distress. Cardiovascular examination reveals regular rate and rhythm with normal S1 and S2; no murmurs, rubs, or gallops are heard. Jugular venous pressure is not elevated. Lungs are clear to auscultation bilaterally. There is no peripheral edema. Resting ECG shows normal sinus rhythm with no ST-segment changes and no Q waves.
Which of the following is the most likely diagnosis?