Compared with uncoated grafts, vascular prosthetic grafts coated with heparin exhibited significantly reduced calcium content 5 months after subcutaneous implantation in rats. Likewise, coating a portion of a porous polyurethane graft with sulfonated poly(ethylene oxide) reduced platelet adhesion and dissolved calcium in a canine right ventricle-pulmonary artery shunt model compared with the uncoated portion. These findings are thought to reflect the non-adhesive and mobile characteristics of poly(ethylene oxide), as well as the negative charge of sulfonate acid groups. However, both types of coatings were associated with increasing calcium deposition over time, suggesting that the coatings delayed but did not abolish the calcification process. This is due to the fact like bone formation, calcification is an active process that progressives over time and cannot be hindered by passive measures.