Abstract
The graft is normally well accepted by the host and becomes firmly united along its upper and lower margins by fibrous tissue which covers the sutures and smooths out the junctions. There is almost no immune reaction to the dead foreign tissue and rejection problems do not arise. The most notable feature is the thickening of the bases of the cusps. As this extends, it will probably limit the useful life of these grafts, although they provide a valuable alternative to the man-made prosthesis.