The efficacy of chitosan post-treatment of glutaraldehyde-treated porcine pericardial substitute for the prevention of postoperative epicardial reaction and adhesion formation in mongrel dogs has been assessed. Glutaraldehyde (0.625%)-treated porcine pericardium showed moderate to dense adhesions to the heart and other underlying organs with moderate to severe epicardial reaction. None to minimal epicardial reaction without adhesion was observed in glutaraldehyde-treated porcine pericardium post-treated with chitosan at 5 months. Presumably, chitosan post-treatment prevents the slow release of residual glutaraldehyde and reduces the toxicity of the glutaraldehyde-treated implants, minimizing the chance of adhesion formation and epicardial reaction.