We studied 59 pregnancies in 48 female carriers of prosthetic heart valves. In 44 pregnancies the mother had a metal valve mostly with coumarin therapy and in 15 a bioprosthesis usually without hematologic treatment. In the patients with metal prostheses we had the following maternal complications: 1 maternal death, 3 valve thromboses, 2 heart failures and puerperal hemorrhage. There was also a significantly increased rate of preterm, low birth weight infants and intrauterine growth retardation. Concerning malformations we found only 2 cases of mild nasal hypoplasia. Regarding the complications of bioprosthesis, we had only 1 case of paroxysmal tachycardia and no fetal complications. Comparing the results we came to the conclusion that pregnancy is much better tolerated in patients with bioprostheses and that in patients with metal prostheses the risk is increased if the mother is older than 30 years, if time of replacement is more than 5 years or if there is a history of previous thromboembolism or gravidic heart failure.