Obstructive sleep apnea (OSA) is an important public health concern, which affects around 2-4% of the population. Left untreated, it causes a decrease not only in quality of life, but also of life expectancy. Despite the fact that knowledge about the mechanisms of development of cardiovascular disease in patients with OSA is still incomplete, observations confirm a relationship between sleep disordered breathing and the rheological properties of blood. One possible consequence of an increased incidence of cardiovascular disease may be a rise in mortality in OSA patients. Continuously improved research methods are allowing for an increasingly more accurate understanding of the significance of observed changes.