Abstract: A process for treating bovine pericard tissue to increase resistance to biological degradation by wet-chemical processing, The wet-chemical processing consists essentially of: (i) separating any adherent fat and basal membrane from the tissue; (ii) contacting the tissue with an aqueous, alkaline solution of sodium hydroxide, potassium hydroxide, lithium hydroxide or sodium carbonate to swell the tissue; (iii) contacting the swollen tissue with an aqueous sodium chloride solution to control the swelling; (iv) contacting the tissue with a solution of a metal-ion complexing agent with a pH in excess of 11; and (v) contacting the tissue with an aqueous buffer solution having a pH of 4.5 to 6.0. Each of steps (ii)-(v) is followed by a water rinse. The pericard tissue is then dried and sterilized.