Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Portable AP upright chest radiograph is obtained . EKG lead and external pacer leads are noted as well as midline sternotomy wires and mediastinal clips . The lung volumes are low , but the lungs appear clear . No definite sign of pneumonia or CHF . No pleural effusion or pneumothorax is seen . A retrocardiac density is compatible with known hiatal hernia . Imaged osseous structures appear intact .
    OUTPUT:
    
Hiatal hernia , otherwise unremarkable study .