Cardiac valve allografts 1962 - 1987; current concepts on the use of aortic and pulmonary allografts for heart valve substitutes; [proceedings of the Symposium on Current Concepts on the Use of Aortic and Pulmonary Allografts for Heart Valve Substitutes, Berlin (West), September 7 - 9, 1987] (Steinkopff [u.a.], 1988)