A 17 year old female presents to the ED with a 1-week histor…

A 17 year old female presents to the ED with a 1-week history of left leg pain and swelling. She reports she takes oral contraceptives. Evaluation with Doppler ultrasound reveals absence of flow in the left femoral and popliteal veins.  The most important potential complication one should be cautious about with this patient is: