Many have hypothesized that both chemical and mechanical material properties are important in the design of a small bore vascular graft. In an attempt to address both issues, a xenogeneic graft crosslinked by photo-oxidation and covalently modified with heparin was developed. The compliance, burst strength, and suture pull strength of photo-oxidized (PhotoFix®) and heparin-modified photo-oxidized ovine carotid tissue were tested in vitro. The heparin modification process was found to have no statistically significant effect on any of these properties. The shrink temperature of fresh, photo-oxidized, and heparin-modified photo-oxidized tissue was assessed using DSC. A small increase in the shrink temperature of the heparin-modified photo-oxidized tissue over the fresh tissue was found to be statistically significant (P < 0.05). In vivo assessment of unmodified, heparin-soaked, and heparin-modified PhotoFix ovine grafts indicated that covalent modification of the grafts was imperative for the graft’s success.