A new synthetic approach for the preparation of segmented polyurethaneurea (SPUU)–PEO–Heparin graft copolymers (B–PEO–Hep) has been developed. The procedure involved the coupling of hexamethylene diisocyanate (HMDI) to soluble Biomer® (B) through an allophanate/biuret reaction. The free isocyanate (NCO) groups attached to Biomer® were then coupled to PEO terminal hydroxyl groups to form PEO grafted Biomer® (B–PEO). B–PEO free hydroxy groups were modified with HMDI to introduce terminal isocyanate groups. The NCO functionalized B–PEO was then coupled to heparin (Hep) functional groups (OH, NH2) producing B–PEO–Hep graft copolymer. Synthetic intermediates were confirmed by FTIR, NCO group determination, and toluidine blue heparin assay. Physical characterization techniques, such as contact angle measurements, water swelling, light scattering measurements, and DSC thermal analysis, detailed properties of the graft copolymer containing covalently bound heparin. This new heparinized copolymer can be applied as a coating on other existing blood contacting surfaces without changing bulk properties. The heparin bioactivity observed attests to the usefulness of this new procedure as a coating to improve the blood compatibility of blood‐contacting surfaces.