Increasing clinical experience has led to a world wide expansion of glutaraldehyde fixed aortic heterografts for valve replacement in patients. The distinct advantage of this valve is a very low rate of thrombembolic complications during the postoperative course. In our hospital 324 such prostheses of the types Hancock and Carpentier have been implanted in 290 patients. In 154 cases follow-up 6 months to 3 years after the operation have been obtained. Thrombembolic complications occured in 1,4%. Other postoperative complications were hepatitis (13,4%), and valvular endocarditis (1,5%). Postoperative control of patients after isolated mitral or aortic valve replacement revealed improved clinical conditions in 90,9%. Dysfunctions of the valve have not been observed. For aortic valve replacement prostheses of a diameter of 27 and 29 mm have been used. In mitral and tricuspid position generally size 31 mm and 33 mm valves were implanted. The decision to use glutaraldehyde fixed biological valves requires the observation of long time results demonstrating reliable mechanical stability of such valves for some decades.