Since July, 1970, 111 patients have undergone mitral and/or tricuspid valve replacement with a glutaraldehyde-fixed porcine xenograft mounted on a flexible stent; 41 of these patients also had aortic valve replacement with a Starr-Edwards or Bjork-Shiley valve, and 85 patients presently are alive. Cumulative follow-up totals 2,060 months, with 16 patients followed more than 4 years. Anticoagulants have not been administered postoperatively, and one patient has had a systemic embolus. Postoperative hemodynamic assessments have been carried out in 54 patients, and in either the mitral or tricuspid position the valve was shown to have good hydraulic function. Significant mitral regurgitation, secondary to prosthetic dysfunction, occurred in one patient 56 months following implantation. Progressive prosthetic stenosis has not occurred, and hemolysis or anemia of clinical significance has not been observed as a consequence of the use of the use of the xenograft. To date, these clinical and hemodynamic data indicate that the glutaraldehyde-fixed xenograft, mounted on a flexible stent, is the prosthesis of choice for mitral and tricuspid valve replacement.