a method for making a blood - contacting medical device with improved biocompatibility by applying to the blood - contacting surface an aqueous solution of heparin and then overcoating the heparin with a porous polymer . the inclusion of a porous polymer in intimate contact with a heparin on the device controls the administration of heparin following implantation or other blood contact . the adhesion of the coating and the rate at which the heparin is delivered can be controlled by the selection of an appropriate bioabsorbable or biostable polymer .