In this study, an attempt was made to investigate whether prostaglandin (PG) synthesis inhibitor (PGSI) can improve hypotension during cardiopulmonary bypass (CPB). The mean systemic blood pressure (SBP), the blood base excess (BE), the urine output and the dose of metaraminol were estimated. Administration of PGSI during CPB improved hypotension and increased urine output without impairing peripheral circulation.