A 60-year-old man presents to the outpatient cardiology clinic for follow-up. He has a history of a three-vessel coronary artery bypass surgery (CABG) following a small myocardial infarction 10 years ago, insulin-dependent type II diabetes mellitus, peripheral arterial disease, and active smoking. Due to activity-limiting angina that interfered with his quality of life, metoprolol tartrate was increased from 50 mg to 75 mg twice a day at his last visit two months ago, and he was continued on isosorbide mononitrate 60 mg daily, ranolazine 500 mg twice a day, and amlodipine 5mg daily. Despite this regimen, he continues to report angina almost daily with physical activity of moderate intensity. He reports mild orthostatic lightheadedness. On exam, his heart rate is 78 beats per minute (bpm), blood pressure 100/70 mm Hg while sitting, respiratory rate 16, and oxygen saturation is 98% on ambient air. His physical exam is within normal limits without clinical signs of heart failure. His electrocardiogram shows sinus rhythm at a rate of 80 bpm with non-specific diffuse ST changes, unchanged from prior tracings. A dobutamine stress echocardiogram performed off metoprolol at his last visit showed normal resting systolic function with a small stress-induced anteroseptal wall motion abnormality at 100% of his maximum predicted heart rate.