Coronary artery spasm (coronary spasm) is an abnormal contraction of an epicardial coronary artery resulting in myocardial ischemia and its incidence is relatively high in Japanese as compared with Caucasians. Coronary spasm occurs most often from midnight to early morning when the patient is at rest and it is usually not induced by exercise in the daytime. Coronary spasm can be induced by acetylcholine, an endothelium-dependent vasodilator which causes vasodilatation in the normal coronary artery. Spasm artery is hyperresponsive to the vasodilator effect of nitroglycerin, an nitric oxide (NO) donor and is deficient in NO activity. The major risk factor for coronary spasm is cigarette smoking. Coronary spasm can be a cause of not only variant angina but also ischemic heart disease in general, including unstable angina, acute myocardial infarction and sudden ischemic death.