DefinitionDeep venous thrombosis is a condition in which a blood clot forms in a vein that is deep inside the body.Alternative NamesDVT; Blood clot in the legs; Thromboembolism; Post-phlebitic syndrome; Post-thrombotic syndromeCauses, incidence, and risk factorsDeep venous thrombosis (DVT) mainly affects the large veins in the lower leg and thigh. The clot can block blood flow and cause swelling and pain. When a clot breaks off and moves through the bloodstream, this is called an embolism. An embolism can get stuck in the brain, lungs, heart, or other area, leading to severe damage.Blood clots may form when something slows or changes the flow of blood in the veins. Risk factors include:After a pacemaker catheter has been passed through the vein in the groinBedrestCigarette smokingFractures