OBJECTIVE Gastrointestinal (GI) complications following cardiac surgery are uncommon but may be life-threatening. The aim of this prospective study is to determine the incidence, independent risk factors, and outcomes following GI complications after cardiac surgery. METHODS Between March 2006 and February 2011, postoperative GI complications were diagnosed in 35 of 7175 consecutive patients who underwent cardiac surgery. Preoperative, intraoperative, and postoperative predictors of complication and death were identified and compared with a control group. We also sought to compare the incidence of GI complications in patients undergoing on-pump and off-pump cardiac surgery. RESULTS GI complications occurred in 35 (0.48%) patients including upper GI bleeding (29, 82.8%), intestinal ischemia (3, 8.5%) perforated duodenal ulcer (1, 2.8%), volvulus of sigmoid (1, 2.8%), and also one patient (2.8%) had upper GI bleeding because of gastric tumor. Patients in the GI group were an average of 5 years older than patients in the control group (P=0.011). In the on-pump group, 32 (91.4%) patients experienced GI complications, compared with 3(8.6%) in the off-pump group (P=0.011). The incidence per type of procedure was as follows: coronary artery bypass grafting (CABG) (51.4%), single or multiple valve surgery (17.1%), congenital disease (14.2%), combined CABG and valve (8.6%), aortic surgery (5.7%) and the pulmonary artery embolectomy (2.8%). By logistic multivariate analysis, twelve parameters were identified that predicted GI complications: age greater than 65 years, low left ventricular ejection fraction (EF<30%), preoperative creatinine>1.5 mg/dL, on pump operation, prolonged time of cardiopulmonary bypass (CPB), prolonged time of aortic cross clamp, congenital heart disease, aortic dissection, use of intraaortic balloon pump (IABP), blood transfusion, hypotension, and sodium bicarbonate use. Surgical treatment was used in 7 patients (20%) with GI complication. The mortality rate in the surgical group was 85.7% and was the highest in patients who had intestinal ischemia (42.8%). The overall hospital mortality among patients with GI complications was 62.8% (N.=22) compared with a mortality rate of 2.9% (N.=10) in patients without postoperative GI complications (P=0.000). CONCLUSIONS GI complications are an infrequent, but serious consequence of cardiac surgery and high index of suspicious is required for their detection. Furthermore, successful outcome can be enhanced by improving cardiac output, prompt diagnosis and early surgical intervention.