Cerebrovascular stroke is one of the major complications in cardiovascular surgery with cardiopulmonary bypass. The purpose of this study was to evaluate the usefulness of preoperative 99mTc-ethyl cysteinate dimer (ECD) SPECT and acetazolamide (diamox) enhancement to predict neurological complications in cardiovascular surgery. Eighteen patients with coronary disease, valvular disease or aortic aneurysm were studied before the operations. Regional cerebral blood flow and perfusion reserve were evaluated using ECD SPECT before and after the intravenous administration of diamox (1 g). Three cases with moderate to severe baseline abnormalities and poor perfusion reserve had cerebral infarction postoperatively. Twelve cases with good to fair perfusion reserve had no neurological complication. Three cases having poor perfusion reserve had the operations with more intensive brain protection, in which higher perfusion pressure to the brain was maintained during cardiopulmonary bypass, and no neurological complication was observed. In conclusion, patients who have moderately or markedly abnormal baseline flow with poor perfusion reserve may have some risk of neurological complications in cardiovascular surgery. ECD SPECT with diamox enhancement may give information useful for selection of operation procedures.