The failure mode of autologous pericardial tissue valves (Autogenics^R) was studied by means of histological methods and compared with the degeneration pattern of heterologous pericardial valves. Autologous heart valves failed due to cuspal tears at the commissural area, while heterologous heart valves exhibit severe calcification of the pericardium. High biocompatibility of autologous tissue valves is indicated by the absence of calcium deposits, macrophages and foreign body giant cells and the presence of endothelial cell ingrowth. Severe disintegration of autologous tissue suggests that brief immersion in glutaraldehyde generates inadequate mechanical stability of bioprosthetic heart valve material. Heterologous valves exhibit low biocompatibility but superior preservation of the collagenous biomaterial.