Angina pectoris is a clinical syndrome of discomfort in the chest, jaw, arm, or other sites which is associated with myocardial ischaemia. The nature of angina has many individual variations, and it is easier first to consider the typical syndrome. It is hard to better the descriptions of William Heberden: There is a disorder of the breast, marked with strong and peculiar symptoms, considerable for the danger belonging to it.... Those who are afflicted with it are seized, while they are walking, and more particularly when they walk soon after eating, with a painful and most disagreeable sensation in the breast.... the moment they stand still all this uneasiness vanishes. After it has continued some months, it will not cease so instantaneous upon standing still ... (most) whom I have seen, who are at least twenty, were men, and almost all above 50 years old, and most of them with a short neck, and inclining to be fat.... But the natural tendency of this illness be to kill the patients suddenly.... The os sterni is usually pointed to as the seat of this malady ... and sometimes there is with it a pain about the middle of the left arm. The usual cause of myocardial ischaemia is coronary atherosclerosis. Other diseases of the coronary arteries (emboli, spasm, vasculitis, Kawasaki disease, congenital anomalies), other cardiac diseases (hypertrophic cardiomyopathy, severe hypertension, severe aortic valve disease), and high output states (severe anaemia, thyrotoxicosis) are all uncommon or rare causes of angina. However, while angina is usually associated with atherosclerotic coronary artery disease, the converse is not always true. The condition of coronary atherosclerosis is very common (fatty streaks and more advanced plaques are almost universal in adults in industrialised countries) but it does not always cause myocardial ischaemia. Furthermore, myocardial ischaemia may present other than with angina - for each presentation there is a wide differential diagnosis.