The visual disturbances of 45 patients following open heart surgery could be divided into disturbances of (1) visual acuity, (2) visual accuracy, and (3) visual reality testing. The non-hallucinatory phenomena consisted mainly of loss of colour vision, metamorphopsias, visual gnostic disorders and cortical blindness. The hallucinatory phenomena could be divided into the delirium type of hallucinations with clouding of consciousness and the spectator type of hallucinations with a clear sensorium. The causes of the visual symptomatology and cardiac psychoses are seen in microembolization and/or ischemic hypoxia. The basal ganglia and the occipital lobe are areas of predilection for embolic and hypoxic changes. Identical psychoses also occur in cerebral malaria and polycythemia vera which show the same embolic and anoxic neuropathological changes of vascular occlusion as do many patients who die following open heart surgery with extracorporal circulation.