This book is timely and challenging. Within its pages are commentaries and opinions on the scientific background and explanatory ideas for a complex of symptoms and investigations known as syndrome X. The commonest cause by far of angina pectoris is coronary artery obstruction due to atheromatous lesions both within the wall of the artery and intruding into the lumen; in such patients it is expected that there maybe ST segment depression on atrial pacing or on an exercise test indicating myocardial ischemia. Syndrome X was a term first used in an editorial written by Kemp in 1973. He was referring to patients in group X in a paper from Arbogast and Bourassa. Patients in group X had three features, namely angina as judged on a clinical history, alterations of the ST segment on the electrocardiogram during atrial pacing and smooth unobstructed coronary arteries (presumed normal) as assessed by the technique of coronary angiography. The changes on the electrocardiogram, conventionally indicative of myocardial ischemia, could not be explained on the basis of any abnormality of the coronary arteries and Kemp named the complex of fmdings syndrome X because of this seeming paradox and the lack of a single explanation. In the last thirty-one years there has been substantial scientific interest in this syndrome giving rise to a large number of publications. The name syndrome X has led to considerable confusion. Physicians are familiar with the X chromosome and with X linked congenital disorders.