Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Single AP view of the chest was obtained . Cardiomediastinal and hilar contours are stable with moderate cardiomegaly . There is no pneumothorax . Again seen is a left retrocardiac opacity , which may represent atelectasis or pneumonia . The right lung is clear . Pulmonary vasculature is within normal limits .
    OUTPUT:
    
Left basal atelectasis or pneumonia . A lateral view is recommended for better assessment .