IntroductionAngina is classically known as ischemia of the myocardium induced by stenosis of epicardial coronary arteries. It is characterized by a range of symptoms, including chest pain, palpitation, and breathlessness [1][2][3] . However, half of patients do not have significant organic stenosis (≥ 50%) of epicardial coronary arteries who undergo coronary angiography (CAG) for clinical symptoms likely to angina or possible myocardial ischemia [4][5][6] .In 2017, Bairey et al. coined the term ischemia with nonobstructive coronary artery disease (INOCA) 7) , and INOCA has since received increased clinical attention worldwide. In 2020, the European Association of Percutaneous Cardiovascular Intervention (EAPCI) proposed the first expert consensus regarding INOCA, which recommended a universal defi nition 8) . Subsequently, in 2023, the Japanese Circulation Society (JCS) published guidelines concerning the recommended diagnosis and medical treatment of INOCA 4) . In 2023, the American Heart Association (AHA)/American College of Cardiology (ACC)/ American College of Chest Physicians (ACCP)/American Society for Preventive Cardiology (ASPC)/Preventive Cardiovascular Nurses Association (PCNA) guidelines were also published on how to diagnose and treat INOCA 9) . Numerous clinical data are available on angina with nonobstructive coronary arteries. For example, the concept of coronary microvascular flow reserve was established in the 1980s 10-12) . However, several problems associated with INOCA yet remain unresolved. We herein review the current consensus on the definition, pathophysiology, epidemiology, diagnosis, and treatment of INOCA.
Definition of INOCAINOCA is defi ned by three criteria: (1) stable, chronic, and typical anginal chest symptoms; (2) objective findings of myocardial ischemia; and (3) no flow-limiting epicardial stenosis 4,7,8) . Chronic symptoms can last for several weeks 4,7,8) .Ischemia can be clinically detected by electrocardiography (ECG), echocardiography, cardiac magnetic resonance imaging, nuclear medicine imaging, and increased myocardial lactate production during the coronary spasm provocation test 1-4, 13, 14) .Flow-limiting stenosis includes ≥ 50% organic stenosis and stenosis with a fractional fl ow reserve (FFR) ≤ 0.80 4,7,8) .Myocardial ischemia with significant epicardial stenosis is called ischemia with obstructive coronary artery disease