Important pathophysiological mechanisms in obstructive sleep apnea at night are increasing pleural pressure swings, hypoxia and hypercapnia, as well as central nervous arousals with consecutive fragmentation of regular sleep structure. They influence the cardiovascular system, at first only at night and at a later stage also during the day. This might result in cardiac structural changes: dilation and hypertrophy of the right ventricle, hypertrophy of the left ventricle, (especially of the muscular ventricular septum), dilation of right and left atrium. It is suggested that these cardiac structural changes are characteristic for obstructive sleep apnea and therefore define the "sleep apnea heart".