We present the evolution of venous tissue, used as a mitral or tricuspid prosthesis or in the reconstruction of the right ventricular outlet tract, for periods of up to 18 months. A histological and hydrodynamic study is made of the valves after sacrificing the animals. The venous tissue showed fibrosis, structural disorganization, elastosis, elastorexis and, above all, intense calcification in heavy deposits. Since the venous tissue evolved toward fibrosis and calcification, its use is considered contraindicated.