A 33-year-old woman presented with central pleuritic chest pain and a nonproductive cough. She was normally physically active without exercise limitation, but for the past 2 days she had felt short of breath with any exertion. Five months earlier, she had delivered a healthy baby boy; her pregnancy and delivery had been uncomplicated. She was a reformed IV drug user and had a 20-pack-year smoking history. The patient was raised in New Mexico, but for the previous 2 months had been visiting her mother in Vancouver, BC, Canada. Occupational and family histories were unremarkable.