Venous thromboembolism (VTE) refers to a blood clot that begins in a vein. It is the third largest vascular diagnosis after a heart attack and stroke, affecting between 300,000 and 600,000 Americans each year. There are two types: Deep vein thrombosis (DVT) Deep vein thrombosis is a clot in a deep vein, usually in the leg. DVT sometimes affects the arm or other veins. Pulmonary embolism (PE) A pulmonary embolism occurs when a DVT clot breaks free from a venous wall, travels to the lungs, and then blocks some or all of the blood supply. Blood clots from the thigh are more likely to rupture and reach the lungs than blood clots in the lower leg or other parts of the body.