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Sudden cardiac death is the leading cause of death in industrialized countries, accounting for 10 to 20% of total mortality. Several studies have demonstrated a circadian variation of sudden death with a primary peak in the morning hours after awakening and a secondary peak in the late afternoon. Weekly and seasonal variations have been observed, with more frequent occurrence of sudden death on Mondays and in the winter compared with other days of the week and seasons, respectively. These patterns of disease occurrence indicate the presence of identifiable triggering factors. Interestingly, the circadian pattern of sudden death appears to be more pronounced in older patients and to be attenuated by ß-blocker therapy. Rupture of an atherosclerotic plaque with subsequent coronary thrombosis is the most common underlying pathophysiologic mechanism of sudden death. The variation in disease occurrence may reflect endogenous physiologic rhythms and the importance of external events (eg, exertional physical activity) that trigger changes (eg, surges in blood pressure) that lead to coronary plaque rupture. To reduce the long-term risk of sudden death, strategies of primary and secondary prevention must be further developed. To reduce short-term risk of sudden death, patients at risk for sudden death may require additional behavior modification and pharmacological intervention.