Abstract: The present invention provides a method of treating human cardiac valve dysfunction, by replacing the existing valve with a novel bioprosthesis of the present invention which comprises a marine mammal ventricular outflow (aortic or pulmonary) valve. The marine mammal ventricular outflow valve is treated by a fixative agent to sterilize, fix, increase the strength of the leaflets and lessen the antigenicity of the tissue valve. Following this step, the marine mammal ventricular outflow valve can either be stent-mounted or can be unstented. The stent-mounted marine mammal ventricular outflow valve can be used to replace a human aortic, mitral, or tricuspid valve, while the unstented marine mammal ventricular outflow valve can be used to replace a human aortic or pulmonary valve.