BACKGROUND: The focus of this study is the effects of thiopental sodium, etomidate and propofol on systemic vascular resistance and venous capacitance during cardiopulmonary bypass with constant pump flow. METHODS: Thirty patients (ASA III) scheduled for open heart surgery were randomly divided into three groups. Anesthesia was induced with thiopental sodium 5 mg/kg, fentanyl 5 microgram/kg and vecuronium 1 mg/kg. CPB was conduced with a membrane oxygenator using non-pulsatile flow and moderate hypothermia. When rectal temperature and pump flow had been stable for 5 min, patients randomly received thiopental sodium 4 mg/kg, etomidate 0.3 mg/kg and propofol 2 mg/kg. Perfusion pressure and pump flow were measured 0, 1, 3, 5, 10, 15, 20 and 30 min after administration. RESULTS: The systemic vascular resistance index (SVRI) decreased to 84.3% of the control values after thiopental sodium 4 mg/kg, to 74.7% of the control after etomidate 0.3 mg/kg and to 79.8% of the control after propofol 2 mg/kg. SVRI returned to control value levels 3 min after the administration of thiopental sodium, 20 min after etomidate, and 5 min after propofol. Thiopental sodium, etomidate and propofol reduced venous reservoir volume 1 min after injection and the reduction was sustained throughout the all period of the cardiopulmonary bypass. CONCLUSIONS: The results indicate that thiopental sodium, etomidate and propofol dilate both resistance and capacitance vessels, but there was no correlation between the two vessels.