“…Of the patients who are referred for coronary angiography, with or without ischemia on non-invasive stress testing, 20–50% are found to have angiographically normal coronary arteries [3,49,50]. Despite the absence of epicardial coronary artery disease by angiography many patients suffer recurrent presentations for chest pain [48,50]. There is increasing awareness of pathologies beyond obstructive coronary stenosis that can cause myocardial ischemia, including diffuse epicardial coronary artery disease, occlusion of small secondary branches, microvascular disease, or low baseline resting flow [51,52].…”