A clinical observation of the development of venous thromboembolism in a postpartum patient who had a history of palliative surgery for congenital heart disease is presented. The examination revealed not only a hereditary homozygous mutation of the prothrombin F2: G20210A gene, which increases the risk of venous thrombosis, but also asplenia (congenital absence of the spleen). It has been shown that asplenia (congenital or postoperative) leads to activation of the platelet section of hemostasis, even in the absence of thrombocytosis, and congenital asplenia often accompanies complex congenital heart defects. The authors conclude that it is necessary to treat pregnant women with complex congenital heart defects not only in relation to hereditary thrombophilia, but also the presence of a spleen. With a high risk of venous thromboembolism in pregnant women, the possible longterm administration of indirect anticoagulants is indicated.