A case of cerebral vein thrombosis after cardiac artery bypass grafting is presented in a patient with coronary artery disease and prolonged angina. Postoperatively he failed the weaning trials because of brain dysfunction characterized by confusion, agitation and hyperpnea. He was initially considered to represent a typical case of post cardiac surgery brain underperfusion, but as he later developed persistent signs of endocranial hypertension, imaging of the brain vessels was carried out revealing obstruction of the left transverse and the frontal half of the oblique sinus. The patient was treated with anticoagulation and cerebrospinal fluid drainage through a lumbo-peritoneal shunt. He was discharged from the ICU in good condition after 102 days of hospitalization. As magnetic resonance imaging of the brain is generally recommended in cases with post cardiac surgery brain dysfunction with normal computed tomography scan, adding magnetic resonance phlebography to the examination protocol seems rational.