Five hundred and four St. Jude Medical valves (SJM) were implanted in 435 patients between September 1978 and March 1982. There were 234 females and 201 males with a mean age of 52.8 +/- 10.1 years (range 12-83 years), who underwent 204 aortic, 163 mitral, 67 mitral plus aortic and one triple valve replacements. All patients were followed prospectively. Follow up was 100% complete and averaged 122.2 +/- 1.1 months for operative survivors. The total follow up for aortic patients was 1968.5, for mitral patients 1520.4, and for double valve replacement 573.9 pty. For the entire patient population the total follow up was 4080.8 pty. Early mortality was 2% after aortic, 4.3% after mitral and 5.9% after mitral plus aortic valve replacement. There were 68 late deaths representing a linearized incidence of 1.37%/pty in the aortic, 1.71%/pty in the mitral and 2.61%/pty in the double valve replacement groups. The corresponding cumulative survival after ten years at risk was 85% in the aortic, 78% in the mitral and 72% in the double valve replacement groups. The ten year event-free survival was 64% in the aortic, 57% in the mitral and 47% in the double valve replacement groups. The linearized incidence for thromboembolic events was 3.71%/pty taking all events into account, and 2.67%/pty taking only the first or most severe of several events into account for aortic, 5.1%/pty and 4.08%/pty for mitral, and 6.62%/pty and 5.40%/pty for double replacements, respectively. There were two cases of valve thrombosis, both with proven inadequate anticoagulation. When the prothrombin times measured with the different thromboplastize used in this patient group were converted to INR, the so far homogeneous values could be separated into three groups: INR = 3.0 to 4.5, 2.5 to 3.2 and 1.8 to 2.7. Low INR values caused only a marginal increase in the rate of embolism but a highly significant decrease in the rate of bleeding. These results suggest that the generally recommended INR of 3.0 to 4.5 is too high for the SJM. A large, multicenter, prospective randomized study is therefore proposed to establish the safe INR levels with low intensity anticoagulation after SJM implantation.