Abstract Background Acute gastrointestinal injury (AGI) after cardiopulmonary bypass (CPB) is associated with poor prognosis. This study aimed to evaluate the effect of preoperative probiotic supplementation on the incidence of AGI in patients undergoing CPB procedure. Methods This was a double-blind, randomized controlled trial conducted in a single center. The patients undergoing HVR with CPB between September 2022 and February 2023 were randomly assigned to receive either probiotic (Lac group) or placebo (Placebo group). The probiotic was administered daily for seven days prior to surgery.Univariate and multivariate logistic regression analysis was performed to identify independent risk factors for AGI. A P-value