Background-Stress lesions of the upper gastrointestinal tract are well recognised in adult patients in intensive care. There are no controlled studies of the incidence of these lesions and the effects or side effects of prophylactic treatment in high risk paediatric patients. Methods-79 paediatric patients in intensive care were studied prospectively after operation for congenital heart disease. All patients had at least one endoscopic examination. The first 36 patients were not given prophylactic medication: later 43 children were treated randomly either with pirenzepine (n = 21) or with famotidine (n = 22). Gastric and tracheal secretions were taken daily for culture in those patients given prophylactic medication. Results-Severe inflammation or ulceration of the upper gastrointestinal tract was less common in those patients who were given prophylactic medication (18% v 44%). Prophylactic treatment did not, however, reduce the total incidence of postoperative stress lesions: it shifted the severity of these changes towards mild lesions and reduced the incidence of ulcerations from 25% to 2%. None of the patients developed a pneumonia caused by an organism previously isolated from the stomach. Conclusions-The incidence of stress lesions in children after cardiac surgery resembles that in high risk adult patients. 16-20%. 8-Antacids and H2 antagonists increase the gastric pH to >4. Pirenzepine is an anticholinergic agent that is highly specific for MI receptors of the stomach and reduces the production of hydrogen ions in the gastric mucosa. In addition it improves perfusion of the gastric mucosa, which leads to an increased production of mucus and bicarbonate," but does not change the gastric pH.There is evidence, however, that prophylactic treatment with antacids or H2 antagonists promoted bacterial overgrowth in the stomach and thus increased the risk of nosocomial pneumonia in adults.'2 1 ' Stress-induced ulcers of the upper gastrointestinal tract were detected in infants by pathological examinations in 1926.14 Nevertheless, so far there have been no controlled studies of the incidence of stress lesions and the effects of prophylactic treatment in infants and children in intensive care.'5 The purpose of our study was to obtain reliable data about the incidence of these lesions and about effects and side effects of prophylactic treatment in infants and children who underwent surgery for congenital heart disease.Patients and methods From October 1988 until November 1991 we prospectively examined 79 consecutive children who underwent corrective or palliative surgery for congenital heart disease. We did not include patients who had operations that usually have a short and uncomplicated postoperative recovery such as repair of an atrial septal defect, valvotomy for aortic stenosis, or repair of coarctation of the isthmus. The first 36 patients (group 1) were not given treatment to prevent lesions of the upper GI tract. Later, 43 patients (group 2) were randomised and treated either with pirenzepine, an a...