Coronary arterial spasm has been postulated to be a cause of myocardial ischemia for over 100 years. It was not until the work of Prinzmetal et al in 1959, however, that major clinical attention and research began to be addressed to the role of vasospasm in the manifestations of ischemic heart disease. It is now known that spasm may be clinically important in patients with significant underlying atherosclerotic coronary artery disease as well as in patients with anatomically normal or subcritically stenosed coronary vessels. Research has suggested that spasm may be associated with symptoms of stable resting and/or exertional angina pectoris and that it almost certainly plays a role in the pathogenesis of unstable angina pectoris and acute myocardial infarction. Symptomatic arrhythmias, including sinus bradycardia, heart block, and ventricular tachyarrhythmias, have been documented to complicate coronary vasospasm. Given the potential importance of coronary arterial spasm in so many different ischemic heart disease syndromes, the development of therapeutic agents that may prevent spasm has obvious clinical importance.