Gastrointestinal (GI) complications after cardiac surgical procedures are infrequent but severe. Thirty-three GI complications were identified in 25 patients who underwent cardiac surgery during a 7-year period (2.0% incidence). The mortality rate for patients having these GI complications was 44%. Acute acalculous cholecystitis was the most lethal complication (86%). Acute pancreatitis was the most common complication (eight patients). Most patients responded well to conservative measures. Five patients had upper GI hemorrhage and three had lower GI bleeding that required more than 2 U of packed red blood cells. All patient conditions were diagnosed endoscopically and none necessitated operation. Of the remaining patients, one was operated on because of perforated duodenal ulcer, one because of perforated diverticulitis, and one because of pseudo-obstruction of the colon, and one patient underwent diagnostic laparotomy and showed negative results for presumed acalculous cholecystitis. Liver failure was fatal in all three patients in whom it occurred. GI complications correlated significantly with advanced age, prolonged bypass times, valve surgery, and the female sex. We conclude that septic GI complications--particularly acute acalculous cholecystitis and perforated viscus--after cardiac surgery are uncommon but lethal. Clinical features are often subtle, and a high index of suspicion is necessary for an early diagnosis and the institution of appropriate treatment.