Serious adverse cardiovascular events, including sudden cardiac death, myocardial infarction and stroke exhibit a pronounced circadian rhythmicity, with a significative peak in the early morning hours. Besides circadian rhythm, some reports have demonstrated other period rhythms, as seasonal and weekly, with higher frequencies observed on Mondays and during the winter. The key pathophysiologic process underlying these events is a thrombosis due to rupture of vulnerable atherosclerotic plaques. The main mechanisms involved in this process, such as blood pressure, coagulability and sympathetic activity, demonstrate a circadian rhythm, with higher peaks in the morning. This review will examine the main epidemiological evidences for the rhythmicity of the most serious cardiovascular events.