Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Lung volumes are low . Cardiomegaly persists , and there is no overt pulmonary edema . There is a left retrocardiac opacity , which corresponds with a large hiatal hernia . No pleural effusions or pneumothorax is seen .
    OUTPUT:
    
Left retrocardiac opacity reflects a large hiatal hernia .