a a blood - contacting medical device with improved biocompatibility . the device is coated with a layer of water - soluble heparin , overlaid by a porous polymeric coating through which the heparin can elute . 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 .