Venous thromboembolism is a condition that causes blood clots to develop in the legs, arms or lungs. Up to 13 percent of people with the condition die when a clot travels through the bloodstream and blocks blood flow to the heart or brain. Patients with a history of spontaneous venous thrombosis take the anticoagulant (blood thinner) warfarin (Coumadin) for life to prevent blood from clotting. It has many side effects, including unwanted bruising and bleeding. An intriguing study from Canada suggests that some women who have suffered a spontaneous clot may be at low risk of having another and may perhaps safely discontinue taking warfarin after a few months.