A 25-year-old white female presents to the emergency room because of sharp left-sided chest pain and shortness of breath for the past day. The patient was in excellent health until yesterday. She was awakened from sleep by the sharp left-sided chest pain. The pain worsened with motion and deep breathing. The pain has been increasing in severity and now she has severe left shoulder pain. She reveals having a similar, transient episode of chest pain about one year ago while she was vacationing in Michigan. Presently, she complains of shortness of breath and is very apprehensive about dying. She denies any cough, fever, or sputum production, but has had one episode of hemoptysis earlier today and, upon further questioning, notes some swelling and tenderness of the left calf. She is married and had one normal delivery three years ago. She is taking birth control pills. She has never been hospitalized except for delivery of her first child. The patient does recall having a left ankle fracture 6 years ago with a cast in place for 6 weeks. A review of systems is negative. She denies any history of venous problems. She works as a computer programmer. She has smoked one pack of cigarettes a day for the past eight years. She considers herself a social drinker.