Sleep is an important modulator of cardiovascular function, both in physiological conditions and in disease states. In individuals without a primary sleep disorder, sleep may exert significant effects on the autonomic nervous system, systemic hemodynamics, cardiac function, endothelial function, and coagulation. Some of these influences can be directly linked to specific modulatory effects of sleep stages per se; others result from the natural circadian rhythm of various physiological processes. There is a temporal association between physiological sleep and occurrence of vascular events, cardiac arrhythmias, and sudden death. Epidemiological and pathophysiological studies also indicate that there may be a causal link between primary sleep abnormalities (sleep curtailment, shift work, and sleep-disordered breathing) and cardiovascular and metabolic disease, such as hypertension, atherosclerosis, stroke, heart failure, cardiac arrhythmias, sudden death, obesity, and the metabolic syndrome. Finally, sleep disturbances may occur as a result of several medical conditions (including obesity, chronic heart failure, and menopause) and may therefore contribute to cardiovascular morbidity associated with these conditions. Further understanding of specific pathophysiological pathways linking sleep disorders to cardiovascular disease is important for developing therapeutic strategies and may have important implications for cardiovascular chronotherapeutics.