The term syndrome X is widely used to define patients with typical angina pectoris, normal coronary angiography and demonstrated myocardial ischaemia. The syndrome has multiple causes, it is more frequent in postmenopausal women and there is increased sympathetic tone in many patients. True ischaemia can be demonstrated by metabolic analysis in less than a half of the cases, it is generally of small magnitude and occurs in small segments of the myocardium. It is believed that ischaemia is due to microvascular coronary disease, mainly by endothelial dysfunction. The microvascular dysfunction may have no apparent cause or be associated to factors that injure the endothelium, such as arterial hypertension, diabetes mellitus, insulin resistance, hypercholesterolemia, smoking, oestrogen deficiency and incipient atherosclerosis. The main explanations to cases without true ischaemia are altered pain perception, psychic disturbances and cardiac metabolic abnormalities that can to generate pain and electrocardiographic alterations similar to ischaemia.