Circadian variations have long been observed in several metabolic functions, many of which are directly or indirectly related to the cardiovascular system and its pathophysiology. Recent reports linking circadian patterns to the development of symptomatic and asymptomatic myocardial ischemia, sudden cardiac death and myocardial infarction raise important questions concerning the mechanisms of myocardial ischemic activity in patients with coronary artery disease, and they have implications for prognosis, therapy and further research.