Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Midline sternotomy wires and a prosthetic cardiac valve are again seen . Lung volumes are low with overlying EKG leads present . Mild retrocardiac opacity is most consistent with atelectasis . No convincing signs of pneumonia . No large effusion or pneumothorax is seen . The cardiomediastinal and hilar contours are stable and normal . Imaged osseous structures appear intact .
    OUTPUT:
    
Limited study with no acute findings . Probable mild retrocardiac atelectasis .