Beginning in March, 1978, 88 patients have had cardiac valve replacements with St. Jude prostheses. There were 26 males and 62 females, aged 6 to 80 years (mean 60). Single valve replacement was done in 67. Double valve replacement was done in 21; 12 of them had two St. Jude valves and nine had a different second valve. There were 57 mitral and 43 aortic valves replaced. Thirty-six patients had concomitant aorta-coronary bypass, and six others had additional cardiac procedures. All patients have been followed for a total of 807 patient-months (mean 9 months). Seventy-nine have been receiving sodium warfarin and seven are not receiving anticoagulants. There has been one embolic episode. There are no valve failures to date. Early mortality is 2.3% and late mortality, 5.7%; no death was valve related. Fifty-three survivors have improved by two or more N.Y.H.A. classifications. Fifty-four valves studied postoperatively at rest, during pacing, and during isoproterenol infusion have demonstrated significantly better hemodynamic performance than have mitral porcine xenografts studied in an identical manner (p < 0.05). Phonocardiography, M-mode and two-dimensional echocardiography, and cinefluoroscopy, carried out in 18 patients, have proved to be reliable noninvasive techniques for long-term follow-up. This experience indicates that the St. Jude prosthesis offers an excellent and predictable alternative in the surgeon's decision-making concerning valve choices.