Where is the ideal heart valve substitute? What has frustrated its realization?

Laboratory and clinical experience in cardiac valve operations and use of imperfect but serviceable valve substitutes over the past four decades have framed the general specifications for an ideal heart valve substitute. This report covers four major aspects of prosthesis characteristics. (1) Implantability: Essentially stable, viable tissue-to-prosthesis linkage is achievable with a porous fixation element. (2) Hemodynamics: Minimal resistance and efficient opening and closing are best attained with bioprostheses and homografts. (3) Thromboembolism: Thromboembolism is a persistent problem with mechanical valves. It is minimized by biological valves and abolished, experimentally, by appropriately encapsulated implants. (4) Durability: Mechanical valves are best. Tanned bioprostheses undergo "spontaneous degeneration"; untanned homografts are a little better. Knowledge and technology are needed to develop a synthetic leaflet membrane that possesses inherent physical, visco-elastic-rheologic properties of natural valve leaflets and is compatible with natural healing processes.