Objective To eveluate the effects of selected decontamination of the digestive tract (SDD) on intestinal flora and intestinally derived endotoxemia in patients of rheumatic heart disease undergoing valve replacement operation with cardiopulmonary bypass (CPB) and the clinlical sigeficance. Methods Twenty-eight adults were randomly divided into the control group and the treatment group. Patients in the control group took preoperative preparation routinely while those in the treatment group were orally administrated with Tobramycin (100 mg), Garlicin (40 mg), and Lactulose (10 ml) three times per day in addition to the routine preoperative preparation. Intestinal floras were detected and the endotoxin levels of arterial blood were measured at four different time points. Results Endotoxin level of patients undergoing CPB increased significantly (P