Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: PA and lateral chest radiographs were obtained . Aeration of the lungs has improved since the last exam . Retrocardiac opacity in the left lower lobe is persistent . Severe cardiomegaly has not changed . The positions of biventricular pacing leads are stable .
    OUTPUT:
    
Stable appearance of severe cardiomegaly and non-specific retrocardiac opacity which could represent atelectasis or infection .