title: [Ultrastructural changes in porcine valve heterografts before and after implantation].
mesh_terms: D000818:Animals; D001021:Aortic Valve / Q000648:ultrastructure*; D001705:Bioprosthesis; D004285:Dogs; D006350:Heart Valve Prosthesis; D013997:Time Factors; D014021:Tissue Preservation