The prognosis of right ventricular failure in patients with mitral valve disease would seem to depend on its chronicity and progression according to the results of a study of 382 cases of mitral valve disease: 231 women, 151 men: average age 55 +/- 13 years, operated between January 1983 and December 1986, most (321) for mitral valve replacement, one third (108) with associated aortic valve replacement. Right ventricular failure was or had been present before surgery in 161 patients: the peri-operative mortality was 11.2% and the secondary mortality 21.7% in these cases, significantly higher than in patients without RVF (respectively 5.0%, p = 0.02, and 8.1%, p < 0.0005). The RVF was present in the immediate post-operative phase in 43 patients, 8 of whom had no signs of this complication beforehand. The cause of this "de novo" early RVF is multifactorial. Ten other patients developed secondary RVF without any obvious cause in 3 cases. The prognosis of "de novo" RVF is very poor (28% survivors at 75 months). At the end of 60.4 +/- 13.6 months 20 patients were lost to follow-up, RVF was present in 60/286 patients followed up. The mortality was high in the patients with residual RVF (38.3% vs 4.0% in patients without: p < 0.0001). This study confirms the poor prognosis of RVF in patients with mitral valve disease whatever the timing with respect to surgery. Right ventricular failure occurring for the first time after surgery is rare (4.7% of cases), of uncertain cause, and carries a particularly poor prognosis.