One hundred and twenty-four patients underwent aortic valve replacement with a nonviable 4°C refrigerated aortic allograft valve. One hundred and eighty-four patients underwent aortic valve replacement with a viable cryopreserved aortic allograft valve in a later era. The longest follow-up was 16 years for the group with the nonviable valve and 11 years for the group with the viable valves. Within this time frame, reoperation was required in 23 patients with nonviable valves for leaflet perforation or rupture whereas no patients in the group with viable valves developed this complication (p<0.0001). The prevalence of endocarditis and thromboembolism was very low in both groups. Viability of leaflet tissue is associated with an important improvement in durability over nonviable allograft valves. Consequently, long-term follow-up results of allograft valves might be best expressed in terms of viability. The current evidence suggests that the viable cells are donor in origin. The viable cryopreserved aortic allograft valve offers significant advantages over current nonviable allograft valves, mechanical valves, and bioprostheses.