The effect of flunitrazepam on circulation and respiration as an anesthetic induction agent was studied in 28 patiens(11women, 17men) undergoing open heart surgery and sortocoronary bypass graft surgery. The body weight varied between 30~69kg and the age ranged from 10~79yrs. They patients were premedicated with diasepam, triflupromasine, hydroxysine, pethidine and atropine in 19 cases, and morphine, hydroxysine and morphine, hydroxysine and atropine in 9 cases. Before the induction of anesthesia, Hartmann's solution was injected to maintaman adequated preload(CVP). Anesthesia was induced with flunitrazepam 0.03mg/kg and pressure pulse and respiratory rate were continuously monitored for 3 mintues. There after morphine 0.3mg/kg and pancuronium 0.1~1.15mg/kg were injected for endotracheal intubation. AFter the injection of flunitrazepam, spontaneous breathing in room ari was maintained in 19 cases even though the respiratory rate was somewhat decreased. The remaining cases were assisted in this respiration with oxygen because of severe respiratory depression or for prophylaxis of hypoxia in angina cases. Arterial blood gas tension showed normal ranges in all cases 3 min after flunitrazepam injection. Pulse rate, systolic and diastolic blood pressure were decreased 8.66%, 16.32%, and 15.9% respectively: however these are still within normal range. And those parameters were increased transiently following intubation as when other induction agents are used. From the above results, it can be concluded that flunitrasepam can be used safely as an induction agent in cardiac anesthesia with adequate preload and ventilation maintenance.