The presence of pericardial adhesions may increase morbidity and mortality during reoperation for cardiac disease. Pericardial substitutes (patches) are commercially available, and reportedly they reduce or prevent adhesions. We implanted five (1984 to 1985) newer pericardial substitutes in dogs. A new polytetrafluoroethylene surgical membrane, two types of glutaraldehyde-stabilized bovine pericardium, formaldehyde-preserved bovine pericardium, and glutaraldehyde-stabilized equine pericardial patches were each implanted in six adult dogs (total 30 dogs) with two dogs from each of the five groups killed at 3, 9, and 18 months. At autopsy the condition of each patch was recorded photographically, and specimens were substituted for histologic examination. Adhesions and epicardial reactions were graded as none, minimal, moderate, or severe. None of the materials produced severe pericardial adhesions, and no adhesions were detected in nine dogs. Eleven dogs had no epicardial reaction and only one showed a severe reaction. Adhesions to portions of the suture line required sharp dissection in 11 dogs. If there is concern over the possibility of calcification in heterologous tissue, polytetrafluoroethylene may be chosen. Patch type did not significantly alter patch behavior.