Abstract： Objective To investigate the effect of acute hypervolemic hemodilution on hemodynamics. Methods Forty-five patients undergone abdominal surgery were enrolled in this study and were randomly allocated into three groups:group H performed with acute hypervolemic hemodilution by 6% HES(hetastareh), group G performed with acute hypervolemic hemodilution by 4% gelofusion (succinyl gelatin) and group C (the control group). After 5 min stabilization period of anesthesia, the baseline hcmodynamic data were collected. Hypervolemic hemodilution procedure was then undertaken in group H or G. Fifteen ml/kg of Ringer's solution(lactated R-L)and 20 ml/kg of colloid were infused in 40 min in all the patients. 6% HES was used in group H, while 4% gelofusion in group G. In group C ,only 15 mL/kg of R-L solution was infused. Heart rate (HR), mean arterial pressure(MAP), central venous pressure (CVP), cardiac index (CI), systemic vascular resistance (SVR) were monitored throughout operation. Hematocrit (Hct) was measured before hemodilution and at each stage of hemodilution. Results At the end of hemodilution, Hct was decreased from 0.385±0.043 to 0.304±0.045 in group H, and in group G, was reduced from 0.395±0.035 to 0.312±0.038. In group H and G, the values of HR, MAP, CI, CVP, SVR were not significantly different (P>0.05) before and after induction of anesthesia compared with those in group C. At time point of 20 minutes after transfusion/expansion and 40 minutes after transfusion/expansion, HR, CI, CVP, MAP in group H, G were higher than those in group C, the differences were statistically significant (P<0.05). In group H after 20 ml/kg expansion, CVP increased to (13.13±3.51) cm H2O (1 cm H2O = 0.098 kPa), and in Group G, CVP increased to (14.88±1.33) cm H2O. Conclusion Preoperative acute hypervolemic hemodilution with 20 ml/kg colloid (6% HES or 4% gelofusion) is well tolerated and safe in 40 min for patients without evidence of heart, lung, liver and kidney disease. Although CVP increases significantly during the period of hypervolemic hemodilution, vasodilatation effect of isoflurane and nitroglycerin can well attenuate the preload of the heart.