This Review is part of a thematic series on Circadian Rhythm and Cardiovascular Function, which includes the following articles: Circadian Clocks and Vascular Function Molecular Time: An Often Overlooked Dimension to Cardiovascular Disease [2009;105:1047–

Abstract: The circadian clock regulates many aspects of physiology, including cardiovascular function. Internal oscillators exist in endothelial, smooth muscle cells, and fibroblasts of the vasculature. Vascular tone and thrombus formation, 2 key elements of vascular function with regard to adverse cardiovascular events, exhibit diurnal rhythmicity. In this review, we describe changes in vascular function that result from genetic disruption of discrete elements of the circadian clock. (Circ Res. 2010;106:833-841.) Key Words: circadian vasculature thrombogenesis vasoreaction Several aspects of cardiovascular physiology and theincidence of cardiovascular events, such as sudden car-diac death, myocardial infarction, unstable angina, ventricular tachycardia, and ischemic and hemorrhagic stroke, are sub-ject to diurnal variation, peaking in the early morning hours.1,2 The early morning surge in blood pressure, accom-panied by a decline in endothelial function, coincides with the peak incidence in clinical cardiovascular events.3,4 The cor-responding oscillations in gene and protein expression of known regulators of vascular physiology highlight the poten