This study of 14 pregnancies in 11 patients with a Starr-Edwards valve prosthesis (nine mitral, two aortic) shows that cardiac functional capacity deteriorated to class III (New York Heart Association criteria) in only 1 woman. The deterioration occurred during the third trimester and the patient's condition improved with medical therapy. Careful medical control diminished the incidence of heart failure in these patients. Six of nine pregnant women with a mitral valve prosthesis were treated continuously with coumarin and three discontinued the therapy gradually before the third trimester of pregnancy. In five pregnant women (three with an aortic valve prosthesis, two with a mitral valve prosthesis) no anticoagulant agents were used. No embolic episodes or severe hemorrhagic complications were seen. One newborn whose mother received coumarin during the first trimester had bilateral hand polydactylia. There were no maternal deaths. One neonate died after fetal stress necessitating the only cesarean section. These results suggest that women with an artificial heart valve tolerate pregnancy well and that anticoagulant therapy is not mandatory in pregnant women with an aortic valve prosthesis, or in the few women with a mitral valve prosthesis not already receiving coumarin at the onset of pregnancy.