Glutaraldehyde (GAF) treatment for biological tissues represents the current standard for cardiac bioprostheses design. An acid-free glyoxal (GAF) fixative devised by the Department of Medical Sciences (University of Turin) allows the obtaining of a more durable tissue, being less prone to calcification after implantation in the human body environment. However, essential requirement in cardiac bioprostheses design is the mechanical performance of the starting material, and each fixation treatment may compromise the tissue structure, consequently deteriorating its mechanical properties. Therefore, the aims of this thesis are (1) to characterize the biaxial mechanical properties of GAF-treated tissue comparing their performances with GLU-treated tissue ones and (2) to determine which treatment produces a more suitable tissue for the bioprostheses.