Between 1970 and 1984, 386 mitral valve replacements with the SE 6120 prosthesis were performed with a mean post-operative follow-up of 75 +/- 44 months or a total follow-up of 2520 patient years (PY). Rapid post-operative mortality was 6.7 percent and the delayed mortality 26.5 percent, the 5-year actuarial survival rate was 80 +/- 2% and that at 10 years 67 +/- 2% (including early mortality). There was no significant difference for survival between single-valve replacements (n = 183) and multiple-valve replacements (n = 203). Multifactorial prognosis analysis (Cox) gave two post-operative prognosis: X (n = 386) = 0.0391 (age) + 0.2421 (NYHA stage); Y (n = 147) = 0.8561 (X) + 0.6299 (VG type). The incidence of complications related to the prosthesis is 4.16 per 100 PY, including sudden deaths. The current actuarial analysis shows that at 5 years 91 +/- 1% at 10 years 78 +/- 2% of the operated subjects are devoid of any such complication and of thrombosis of the valve. Statistically, it was found that permanent atrial fibrillation (p = 0.03), the size of the right atrium (p = 0.02) played a promoting role. With a post-operative follow-up in excess of 8 years. 79% of the survivors are symptom-free or present few symptoms and the myocardial response is poor in 52 patients (NYHA stage III or IV).