Postoperative delirium is an acute and fluctuating state of confusion and disorientation with an incidence of 25-70% after cardiac surgery. Possible reasons for this multifactorial complication are hypoperfusion, cerebral microembolization and inflammatory response, which eventually lead to regional or global imbalance between cerebral oxygen demand and supply. Adequate cerebral blood supply depends sufficient blood supply via the vertebral arteries and the internal carotid arteries. The aim of this preliminary study is to investigate if patients who develop delirium after open-heart surgery show differences in their cerebral blood flow during cardiopulmonary bypass (CPB) in extracerebral arterial vessels compared to those patients without delirium.