A 27-year-old woman with a mechanical heart valve suffered multiple thromboembolic events while pregnant despite anticoagulation with high-dose heparin. Warfarin, the anti-coagulant of choice for patients with prosthetic heart valves, is teratogenic and can cause hemorrhagic complications at delivery. Heparin reduces thromboembolic complications, but is of uncertain efficacy. We discuss alternatives for the prevention of thromboembolic complications in pregnant women with mechanical heart valves.