The prevalence and complexity of coronary artery disease are growing globally. Despite optimal medical therapy for coronary artery disease, including secondary prevention, and a renewed focus on complete revascularization, an increasing number of patients have refractory, lifestyle limiting angina.1–5 This patient population was formally defined by the European Society of Cardiology Joint Study group on the Treatment of Refractory Angina as patients with “a chronic condition caused by coronary insufficiency in the presence of coronary artery disease, which is not amenable to a combination of medical therapy, angioplasty, or coronary bypass surgery in patients with evidence of ischemia.”3 It has been estimated that 6% to 14% of patients undergoing diagnostic coronary angiography may meet this definition, but there is limited registry data and no coding data available.1,2,5,6 This patient group likely includes a combination of different phenotypes: those patients with incomplete revascularization, those with comorbidities or anatomy that precludes further revascularization, and those with microvascular dysfunction in addition to epicardial disease.