Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The lung volumes are low . The patient is status post CABG with median sternotomy wires and mediastinal clips noted . Clips in left upper quadrant are appreciated . A retrocardiac opacity may represent atelectasis or pneumonia in the correct clinical setting . There is no pleural effusion or pneumothorax .
    OUTPUT:
    
A left retrocardiac opacity may represent atelectasis or pneumonia in the correct clinical setting .