Clinical performance of St. Jude and Medtronic-Hall prostheses: a randomized comparative study. Newer and improved models of mechanical prostheses are regularly added to surgeons' armamentarium. This study was designed to compare the clinical performance of two of the most used current models of mechanical prostheses. From August 1983 through July 1985, 182 white patients were prospectively randomized to implantation of the St. Jude Medical (95 patients) or Medtronic-Hall (87 patients) prostheses. There were 84 mitral, 85 aortic, and 13 double (mitral and aortic) valve replacements. There were no differences between the two groups with regard to sex distribution, age, functional class, emergency operation, and site of implantation. Early mortality was 3.2% for patients with the St. Jude valve and 5.7% for those with the Medtronic-Hall (p = NS). The survivors were followed for 3 to 5 years (mean, 4.2 +/- 0.6 years; cumulative follow-up, 559 patient-years). Late mortality was 7.1%/patient-year for the St. Jude group and 3.2%/patient-year for the Medtronic-Hall group (p less than 0.05). However, the valve-related mortality was equal (1.4%/patient-year) for both groups. Noncardiac causes accounted for most of the difference between the St. Jude and Medtronic-Hall groups (2.5%/patient-year and 0.4%/patient-year, respectively). There were no cases of thrombotic obstruction, whereas serious systemic thromboembolism occurred at the rate of 1.8%/patient-year (5 episodes) for the St. Jude group and 2.5%/patient-year (7 episodes) for the Medtronic-Hall group (p = not significant); there were another nine episodes of systemic embolism that left no sequelae. Three patients (St. Jude, 2; Medtronic-Hall, 1), all of whom had aortic valve replacement, required reoperation (0.5%/patient-year) because of prosthetic endocarditis, with two deaths. 