Pulmonary embolism (PE) occurs when venous thrombi are dislodged from their site of formation and embolize to the pulmonary artery circulation. About one-half of patients with pelvic vein thrombosis or proximal leg deep vein thrombosis (DVT) develop PE, which is often asymptomatic. Isolated calf vein thrombi pose a much lower risk of PE. With increased use of chronic indwelling central venous catheters, as well as more frequent insertion of permanent pacemakers and internal cardiac defibrillators, upper extremity venous thrombosis is becoming a more common problem. These thrombi infrequently embolize and cause PE.