Sequential hemodynamic and echocardiographic studies following mitral valve replacement by glutaraldehyde preserved bioprotheses have been carried out in 40 patients. These investigations have been compared to those of patients having received Björk-Shiley or Lillehei-Kaster valves. Between the two groups the data of heart catheterization showed no differences. Echocardiography however showed an earlier normalisation of the data of the left ventricle after replacement by Hancock valves. Therefore and because of low thromboembolic risc and good mechanical stability and low immunogenecity the use of bioprotheses is recommended.