Aortic valves were transplanted from sheep and pigs into the descending thoracic aortas of nine groups of dogs. The valves were fresh, freeze-dried, or treated with propiolactone. Half the groups received azathioprine. The following conditions led to the best results: (1) transplantation of a minimum of aortic wall with the valve; (2) good initial alignment and movement of the cusps; (3) administration of azathioprine for eight weeks; and (4) support of the graft by a Dacron tube, preventing rupture and separating the graft from ingrowing host tissue.
Sweatt JL, Allen CF, Kwong K, Paton BC. Influence of Preparation and Immunosuppression Upon Longevity of Grafted Aortic Valves. Arch Surg. 1970;101(6):658-662. doi:10.1001/archsurg.1970.01340300014004