Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: PA and lateral views of the chest were provided . Subtle retrocardiac opacity is seen , which could reflect pneumonia . No large effusion or pneumothorax is seen . The heart size is normal . The mediastinal contour is unremarkable . The imaged osseous structures are intact .
    OUTPUT:
    
Subtle retrocardiac opacity which could represent an early left lower lobe pneumonia .