A French cooperative retrospective study analysed 155 pregnancies in 103 women with prosthetic heart valves: 95 mechanical prosthesis (MP) and 60 bioprostheses (BP). Among them 13 MP and 10 BP were bivalvular and four were mixed implants. In all, 182 (108 MP and 74 BP) prostheses were exposed to the risk of pregnancy. Among the 108 MP-bearing patients, 16 thromboembolic accidents (TEA) were recorded: 10 thromboses in 13 mitral, two aortic and one pulmonary MP. TEA were four times more frequent under oral anticoagulant therapy. Among the 74 BP, seven suffered premature valve failure. Ninety-nine infants were born to 50 MP-bearing women (53%) and 48 BP-bearing patients (80%) (P < 0.001). Twenty miscarriages were reported; they occurred more often under anticoagulant treatment (17%) than without it (4%) P < 0.02). Coumarin-induced embryopathies were rare (only one definitively identified). Because pregnancy with an MP under anticoagulant therapy is dangerous for the mother and may effect the fetus, the therapeutic indications for women of child-bearing age must be taken into consideration. In a women already with an MP at the time of conception, the duration of heparin therapy should be limited to the following two periods: from the 6th to the 12th week (coumarin-induced embryopathies) and during the last 2 weeks of gestation (haemorrhages during delivery and the neonatal period).