Neurological disturbances were seen in patients who underwent open heart surgery with prolonged extracorporeal circulation. These were found mainly in patients older than 50 years and when episodes of hypotension lower than 50 mm Hg occurred during cardiopulmonary perfusion. A method of recognizing cerebral hypoperfusion would be most helpful to prevent brain damage. According to the experimental and clinical findings of Hager the method of ophthalmodynamography allows some conclusion of analogy in relation to the reaction of the brain vessels. The intraoperative ophthalmodynamogram was recorded in 8 patients undergoing surgery using extracorporeal circulation. The ophthalmodynamograms seen during surgery on the beating heart showed changes associated with surgical manipulation. When the arterial pressure fell the orbital pulsation was decreased. The orbital pulsation stopped when the spontaneous heat beat was replaced by extracorporeal circulation. There was no change attributable to the perfusion pressure produced by the roller pump. Cessation of the orbital oscilogram during extracorporeal circulation does not indicate a cerebral hypoperfusion. No neurological lesion was seen in our patients. We were able to show that amplitude of the ophthalmodynamogram is influenced more by the blood pressure amplitued than the mean arterial pressure.