The use of anticoagulants during pregnancy for prevention and treatment of venous thromboembolism and prevention of systemic embolism in patients with valvular heart disease presents several problems. This article discusses the complications associated with warfarin, unfractionated heparin, and low-molecular-weight heparin as well as the benefits of each. While a literature review turned up only limited data, the authors extrapolated from existing data recommendations for treatment during pregnancy, finding that oral warfarin should be replaced by heparin during pregnancy, especially from the 6th to the 12th week and near term. In addition, treatment recommendations are provided for different stages of pregnancy, delivery, and postpartum.