Circadian variations have been known for a long time for the influence they have on the physiological systems, including the cardiovascular system. The study of the mechanisms with circadian variation that change the function of the cardiovascular system and its diseases has increased greatly in recent years due to its clinical prominence. Through these studies, physiopathology, epidemiology and factors involved in cardiovascular diseases are more understandable. Thus, the incidence of cardiac events has been clearly associated with the morning hours, as well as the possible mechanisms involved in this variation during the daytime hours. The arterial blood pressure, plasma catecholamine levels and cortisol, platelet aggregation, and fibrinolytic system action are the most implicated mechanisms. From this knowledge, it is possible to design new therapeutic strategies that should consider the time of the day of higher risk for the onset of cardiovascular events.