Sudden cardiac death, myocardial infarction, unstable angina, ventricular tachyarrhythmias, fatal pulmonary thromboembolism, rupture of thoracic aorta, and ischemic and hemorrhagic cerebrovascular accidents exhibit a prominent circadian pattern with events more frequently during the morning (0600-1200 h)after awakening. Hematologic processes (e.g. increases in secretion and aggregability of platelets, changes in blood clotting, and fibronolysis), vascular processes (e.g. increase in vascular tone), and hemodynamic processes (e.g. morning surge of blood pressure, secretion of catecholamines, and shear forces) have been implicated in onset of disease. The primary significance of the recognition of circadian variation in the onset of myocardial infarction at any time of the day. Several triggers of the onset of cardiovascular disease have been identified. These include the start of activity in the morning, sexual activity, anger, and heavy physical exertion. However, increasing levels of habitual physical activity have been associated with progressively lower relative risks for cardiovascular events. Through further epidemiologic, clinical, and basic scientific research, we may achieve a better understanding of the mechanisms s that provoke the onset of acute cardiovascular disease. This knowledge will help investigators to devise effective preventive treatments for acute cardiovascular disorders.