Since valve replacement surgery was first employed, research has attempted to create a prosthesis that is safe, durable and effective. A prosthetic valve should not suffer from disadvantages of calcification and premature failure (bioprostheses) or thrombogenicity (mechanical valves). Progress in both design and materials has led to polymer valves being produced and tested in vitro and in vivo, though problems encountered have prevented successful clinical application. In this respect, calcification is a major factor, albeit much less with bioprostheses. New developments in surface modification hold the key to eliminating thrombus and calcification. Early in vivo results are promising; thus, an effective and safe polymer valve may soon become a third clinical option.