Abstract: “PROCESS FOR TREATMENT OF BIOLOGICAL TISSUES”, where an additional step has been added to the conventional biological tissue treatment process—lyophilization—where the material is frozen and then the frozen liquid portion is removed through vacuum sublimation; where a complementary step of tissue reconstitution is obtained through re-hydration of the material with saline solution, thereby evaporating almost all aldehyde residual material resulting in less calcification and increased valve durability after implantation; the application of lyophilization to non-treated, in natura (fresh) bovine pericardium for storage purposes; the application of lyophilization to devices made from treated bovine pericardium; and the application of lyophilization to valve prostheses manufactured from chemically pre-treated pig heart valves.