The release of heparin from monolithic devices composed of different ratios of polyethylene oxide-polypropylene oxide (PEO-PPO) and hydrophobic polyurethane was investigated. The release rate of heparin could be controlled by varying the PEO-PPO content. The heparin release rate from the devices increased as the content of PEO-PPO in the devices increased. The release mechanism may be associated with creation of micro-channels and pores through the devices following the change in the physical structure of the polymer network. Hydrophobic polyurethane containing PEO-PPO can provide an antithrombogenic material for prolonged release of heparin from a heparin blended system.