Surface properties of octavinyl polyhedral oligomeric silsesquioxane (OVS), grafted polyurethane (PU) and heparinized carbon nanotubes (HCNTs) nanocomposite thin-films were evaluated, and the effect of OVS presence on platelet adhesion on the surface of nanocomposite films for artificial heart valve application was investigated using in-vitro tests. OVS was synthesized, then PU and CNT (PU/CNT) nanocomposite films were dipped in the solution of OVS in toluene for grafting. Synthesized OVS was investigated by XRD, FTIR, and NMR tests. SEM-EDX micrographs showed that the morphology of the PU/HCNT surface was obviously changed due to OVS grafting. Surface studies proved OVS grafting on the surface. Surface roughness was increased after grafting PU/HCNT surface with OVS in comparison to the untreated PU/HCNT nanocomposite surface. The contact angle was increased from 88° for PU/HCNT sample to 165° for OVS-grafted PU/HCNT sample. After the addition of CNTs to the matrix, the modulus was increased. According to the MTT test, modified polymeric nanocomposite has no cytotoxicity, and the adhesion of L929 fibroblast cells on the grafted surface was increased. Its shown in the platelet adhesion test that blood compatibility of the OVS grafted films are increased in comparison with PU/HCNT. Surface calcification of OVS-grafted PU/HCNT was reduced according to the in-vitro calcification test. It has been concluded that the combination of physical and mechanical properties of PU/HCNT and the calcification resistance of OVS is a suitable achievement for heart valve application.