[Syndrome X].
The authors reviewed the literature on X syndrome, finding criteria of inclusion/exclusion so different as to often invalidate the results. The syndrome should be diagnosed only in patients with typical anginal pain on effort relieved by nitroglycerin or rest, with perfectly regular coronary vessels and a normal resting left ventricle, without any evidence of variant angina. Other diseases must be strictly excluded (mostly at the esophageal level) and an ischemic process has to be proved by means of more than one provocative test. Interesting pathophysiological findings are the dynamic limitation of coronary flow reserve and frequent reports of a left ventricle dysfunction during stress. Whether these last findings represent an independent entity, an aspect or stage of the variant angina or the initial appearance of a cardiomyopathy, has yet to be clarified. Frequent reports of a higher prevalence of X syndrome in women have not been substantiated and could be explained by many biases.