title: Fundamental basis and clinical validation of frequency analysis of the valve closure sound as an indicator of stiffening of bioprosthetic valves.
mesh_terms: D001021:Aortic Valve; D001705:Bioprosthesis / Q000009:adverse effects*; D006350:Heart Valve Prosthesis / Q000009:adverse effects*; D006801:Humans; D008943:Mitral Valve; D010701:Phonocardiography