Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: A previously identified right middle lobe opacity has resolved . There is increased retrocardiac left lower lobe opacity . No pleural effusion or pneumothorax . Moderate cardiomegaly is unchanged . Median sternotomy wires and mediastinal clips are again seen , likely reflecting prior CABG . Cardiomediastinal and hilar silhouettes are unremarkable .
    OUTPUT:
    
Left lower lobe opacities reflect atelectasis or infection .