Vampire lung

A 33 year old lady with pleuritic chest pain for 3 days comes in and this is her CXR.
What is the major abnormality and what is its significance?

CXR:     Oligaemia of left lung field - signifying less blood perfusing that lung. (Westermark's sign)
Trick:    Stand back sometimes to see things clearer on xrays
Dx:        Pulmonary embolus (affecting main left arterial trunk)
Rx:        O2, fluids, heparin, CT to confirm, consider thrombolytics