 Acute cardiac and vascular events, including sudden cardiac death, myocardial infarction, and stroke manifest a clear surge in the early morning hours around the time of waking, so that their peak onset is between 6 AM and 11AM. The mechanisms for this morning increase in acute cardiovascular events are not fully understood. Factors such as arousal from sleep, increased sympathetic drive, increased vasoconstrictor sensitivity and impaired endothelial function have been implicated. 