Venous thromboembolism (VTE) originates in systemic venous thrombosis and has different etiological mechanisms and natural history from arterial thrombosis. VTE typically originates as deep venous thrombosis in a lower extremity, where it may give rise to acute symptoms “upstream” from the obstructed vein, result in pulmonary embolism, and/or cause chronic venous obstruction. Pulmonary embolism may result in acute respiratory symptoms, cardiovascular collapse and, uncommonly, may also cause chronic disease.