Use with extreme caution.Encyclopedia Entry for Blood Clots :Blood clots. Situations in which a blood clot is more likely to form in veins include: Being on long-term bed rest Sitting for long periods, such as in a plane or car During and after pregnancy Taking birth control pills or estrogen hormones (especially in women who smoke) Long-term use of an intravenous catheter After surgery Blood clots are also more likely to form after an injury. People with cancer, obesity, and liver or kidney disease are also prone to blood clots. Smoking also increases the risk of forming blood clots. Conditions that are passed down through families (inherited) may make you more likely to form abnormal blood clots. Inherited conditions that affect clotting are: Factor V Leiden thrombophilia Prothrombin G20210A mutation Other rare conditions, such as protein C, protein S , and antithrombin III deficiencies. A blood clot may block an artery or vein in the heart, affecting the: Heart (angina or a heart attack) Intestines ( mesenteric ischemia or mesenteric venous thrombosis ) Kidneys ( renal vein thrombosis ) Leg or arm arteries Legs ( deep vein thrombosis ) Lungs ( pulmonary embolism ) Neck or brain (stroke).Clot; Emboli; Thrombi; Thromboembolus; Hypercoagulable state.Deep vein thrombosis - discharge Taking warfarin (Coumadin, Jantoven) - what to ask your doctor Taking warfarin (Coumadin).Thrombus Thrombus Deep venous thrombosis, ileofemoral Deep venous thrombosis, iliofemoral.Anderson JA, Hogg KE, Weitz JI. Hypercoagulable states.