Even after 30 years of experience and success, problems associated wit
h heart valve prostheses have not been eliminated. The most serious pr
oblems and complications are: (i) thrombosis and thromboembolism, (ii)
anticoagulation-related hemorrhage, (iii) tissue overgrowth, (iv) inf
ection, (v) paravalvular leaks due to healing defects, and (vi) valve
failure due to material fatigue or chemical change. Degeneration remai
ns a major concern for long-term success of porcine bioprosthetic valv
es, while there is a more even distribution of failure causes in mecha
nical valves. Direct comparison of the performance of artificial heart
valves is difficult, and it is impossible to categorize any particula
r valve as the best. Nonetheless, clear characteristics can be identif
ied: mechanical valves tend to have greater durability at the expense
of requiring life-long anticoagulant therapy because of their tendency
toward thrombosis, while bioprostheses tend to deteriorate more rapid
ly due to degenerative processes but do not require anticoagulation th
erapy. The choice between bioprosthetic nonthrombogenicity and mechani
cal valve durability depends upon characteristics of the specific pati
ent. Further advances in prosthetic heart valves have three promising
directions: (i) improved nonthrombogenicity with artificial materials;
(ii) improved durability for tissue valves; and (iii) improved hemody
namic characteristics, especially reduction or elimination of low shea
r stress regions near valve and vessel surfaces and of high turbulent
shear stresses along the edges of jets produced by valve outflow or le
akage of flow. Nonetheless, while current artificial valves leave room
for further advances, the superior prognosis for patients with prosth
etic replacement is dramatic and convincing.