Venous thrombosis of the legs is diagnosed by ultrasound. Treatment usually involves medication to thin the blood and dissolve the thrombosis. Two common medications are heparin and coumadin. If patients are not candidates for blood-thinning medication (such as patients with a history of stroke or bleeding), a filter is placed in the large vein leading from the leg to the heart, to catch any clot that may embolize up toward the heart. These filters can be inserted through a catheter inserted in the veins of the groin.