Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The patient is status post median sternotomy and CABG . The cardiomediastinal and hilar contours are stable . Slightly increased opacity at the base of the left lung may represent atelectasis or scarring , but is stable from the prior exam . No pleural effusion or pneumothorax .
    OUTPUT:
    
Subtly increased lung markings in the left lower lobe likely reflect atelectasis or scarring and are unchanged from the prior exam in ___ . Low lung volumes . No definite pneumonia .