Intravenous administration of high dose of fentanyl is gaining wide popularity as the sole anesthetic agent for patients undergoing cardiac surgery because of its favorable characteristics such as, simplicity, stable hemodynamics and supression or modification of stress response to surgery. But some investigators reported the necessity of supplementary anesthetic agent in addition to fentanyl to maintain hemodynamic stability during the surgical procedure. Therefore, we measured the heart rate(HR), systolic blood pressure(SBP), diastolic blood pressure(DBP), mean arterial pressure(MAP), and rate pressure product(RPP) at induction, tracheal intubation, skin incision, and sternotomy time to evaluate the cardiovascular responses to surgical procedure under fentanyl-O2 anesthesia on 12 patients with acquired valvular heart disease. The patients were anesthetized with a loading dose (30ug/kg fentanyl for induction and 1.5ug/ kg/min until sternotomy) followed by continuous infusion of fentanyl (0.3pg/kg/min until the end of cardiopulmonary bypass.) The patients required total doses of 108±4.6ug/kg fentanyl for the entire operation. These measurements were compared with control data (before induction). The results were as followings: 1) During induction (infusion of fentanyl 30ug/kg), HR, SBF, DBP, MAP, and RPP revealed no significant change compared with control data. 2) During intubation and skin incision, HR, SBP, DBP, MAP, and RPP slightly increased but were not statistically significant (p>0.05) 3) During sternotomy, SBP increased from 119.8±16.36 torr to 136.5±15.22 torr, DBP increased from 79.1±12.76 torr to 95.4±10.87 torr, MAP increased from 99.4±13.96 torr to 115.5±12.70 torr, and RPP increased from 10929±2206 torr.beats/min to 13889±2865 torr. beats/min (p<0.05). HR increased from 90.7±8.71 beats/min to 100.2±13.79 beats/min, but was not statistically significant(p> 0.05). 4) One of the patients had recall of the sternotomy and spreading of the chest with the sternal retractor. These data demonstrate that anesthetic doses of fentanyl and O produce minimal change in cardiovascular dynamics during the surgical procedures except sternotomy time. Our findings suggest that fentanyl-O2 anesthesia may be an attractive anesthetic technique in patients with valvular heart disease undergoing valve replacement operations but, will be needed considerations about infusion method, dosage of fentanyl and use of supplementary anesthetic agent according to patients conditions.