Myocardial ischemia has traditionally been related to increased demand, but recent data suggest that intermittent episodes of decreased supply are also important. This article discusses the phenomena underlying the factors that produce spontaneous (non-effort-related) ischemia. These include local arterial phenomena, arterial plaques, endothelial phenomena, neural phenomena, and circadian patterns. The clinical spectrum of myocardial ischemia can be viewed as an interplay among supply, demand, local arterial reactivity, and acute plaque disruption. In addition, neural phenomena and circadian patterns of multiple cardiovascular phenomena combine to make the coronary circulation susceptible to an increased concentration of events in the morning hours, around the time of awakening. With this extension of our understanding of myocardial ischemia, we have reasonable assurance that methods of treatment will advance significantly in the near future.