FINDINGS:
Left upper lobe opacity suggests pneumonia in the given clinical history.
 Retrocardiac opacity is most likely atelectasis from lack of full inspiration.
 No pulmonary edema, pleural effusion or pneumothorax.  The heart size, hila,
 and pleura are normal.

IMPRESSION:
Left upper lobe pneumonia.  Follow-up chest x-ray after treatment to ensure
 resolution.