A 37-year-old woman presents to the emergency department with a swollen, tender left calf and dyspnea. She noted the development of symptoms 3 days ago, the day following her arrival on a plane trip from Austral ia to the United States. She admits to pleuritic chest pain but denies cough or fever, and has no significant past medical history. Her only medication is an oral contraceptive. She does not smoke cigarettes or use alcohol. Her parents are alive; her father takes a “blood thinner” medication for an unknown reason. Examination reveals a diaphoretic white female with tachypnea; positive examination findings include an inspiratory friction rub on the left side of the chest, a swollen left calf with a circumference 50% greater than on the right, and a positive left Homans sign. Vital signs: BP – I 00/60 mm Hg, pulse – I 15 bpm, resp – 26/min, temp 38°C. Pulse oximetry shows 02 saturation on room air of 92%.