Objective:To establish the extracorporeal circulation model of the mongrel dog and to investigate the effect of dextran-40 on inflammation and atrial fibrillation after extracorporeal circulation. Methods:Twelve male mongrel dogs underwent cardiac bypass. Two groups were formed. In experimental group(n = 6),dextran-40 infusion was administered at a dose of 7.5 ml/kg before the initiation of cardiopulmonary bypass and at a dose of 12.5 ml/kg after the cessation of cardiopulmonary bypass. Identical amounts of saline was administered in control group(n = 6). Blood samples were taken from the coronary artery and coronary sinus before bypass,20 min after beginning of bypass,and 4 h,24 h,and 48 h after termination of bypass and initiation of reperfusion. Plasma interleukin (IL)-6,IL-8,IL-10,tumor necrosis factor (TNF)-α,C reactive protein (CRP),troponin I (TnI) were measured in these samples. And heart rate,mean blood pressure,ejection fraction (EF) and cardiac index (CI) were measured at the same time point. Pacing-induced atrial fibrillation was compared between two groups. The t test,χ2 test and ANOVA were used for statistical analysis. Results:In experimental group,lower peak plasma levels of IL-6,IL-8,IL-10,TNF-α,CRP and TnI were found. There was no significant difference in heart rate and mean blood pressure between two groups. Higher figures of the cardiac index and ejection fraction were noted in experimental group. Conclusion:Dextran-40 reduces the systemic inflammatory response,cardiac troponin I release,protects cardiac function and may relieve atrial fibrillation following cardiopulmonary bypass.