Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The lung volumes are slightly low , accentuating the pulmonary vasculature and heart size , which is mildly enlarged . There is hazy opacification in the retrocardiac region in the left lung . Linear scarring / atelectasis in the left mid lung is unchanged . There is no pneumothorax , overt pulmonary edema , or large pleural effusion . Changes related to prior median sternotomy and valve replacement are again noted .
    OUTPUT:
    
Hazy retrocardiac opacity could reflect aspiration or pneumonia in the appropriate clinical setting .