Heterologous pericardia, acquired from mammal, are often used as biological patches in cardiovascular surgery for pericardial substitute, intracardiac defect repair, stenosis enlargement, and change of blood stream direction. However, these biological patches have been clinically encountered with thrombus formation and tissue adhesion, These concerns may be overcome by immobilizing heparin on the surfaces of these biological patches. The study was to evaluate an epoxy-fixed porcine pericardium with ionically- or covalently-immobilized heparin implanted in a canine model as a vascular patch, The nonheparinized counterpart was used as a control, The results obtained suggested that surface-immobilized heparin may reduce thrombus formation and tissue adhesion of implanted biological patches. Additionally, the porcine pericardium with covalently-immobilized heparin was relatively better than its ionically-immobilized counterpart: in reducing thrombus formation and tissue adhesion. Therefore, it is suggested that heparin be immobilized by stable covalent bond in clinical use. The resistance against in vivo degradation for the heparinized tissues (ionically- or covalently-immobilized) was relatively better than the nonheparinized tissue. However, heparinization did not seem to prevent the implanted biological tissues from calcification.