Microvascular Angina: ANGINA PECTORIS or angina-like chest pain with a normal coronary arteriogram and positive EXERCISE TEST. The cause of the syndrome is unknown. While its recognition is of clinical importance, its prognosis is excellent. (Braunwald, Heart Disease, 4th ed, p1346; Jablonski Dictionary of Syndromes & Eponymic Diseases, 2d ed). It is different from METABOLIC SYNDROME X, a syndrome characterized by INSULIN RESISTANCE and HYPERINSULINEMIA, that has increased risk for cardiovascular disease.Angina Pectoris: The symptom of paroxysmal pain consequent to MYOCARDIAL ISCHEMIA usually of distinctive character, location and radiation. It is thought to be provoked by a transient stressful situation during which the oxygen requirements of the MYOCARDIUM exceed that supplied by the CORONARY CIRCULATION.Microcirculation: The circulation of the BLOOD through the MICROVASCULAR NETWORK.Brachial Artery: The continuation of the axillary artery; it branches into the radial and ulnar arteries.Angina, Unstable: Precordial pain at rest, which may precede a MYOCARDIAL INFARCTION.Coronary Circulation: The circulation of blood through the CORONARY VESSELS of the HEART.Endothelium, Vascular: Single pavement layer of cells which line the luminal surface of the entire vascular system and regulate the transport of macromolecules and blood components.Vasodilation: The physiological widening of BLOOD VESSELS by relaxing the underlying VASCULAR SMOOTH MUSCLE.Angina Pectoris, Variant: A clinical syndrome characterized by the development of CHEST PAIN at rest with concomitant transient ST segment elevation in the ELECTROCARDIOGRAM, but with preserved exercise capacity.Microvessels: The finer blood vessels of the vasculature that are generally less than 100 microns in internal diameter.Angina, Stable: Persistent and reproducible chest discomfort usually precipitated by a physical exertion that dissipates upon cessation of such an activity. The symptoms are manifestations of MYOCARDIAL ISCHEMIA.