Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP upright and lateral views of the chest provided . There are midline sternotomy wires , prosthetic cardiac valve and dual - lead pacer unchanged . There is a large retrocardiac opacity which is compatible with known large hiatal hernia . The lungs are clear without focal consolidation , effusion or pneumothorax . The cardiomediastinal silhouette is stable . Bony structures are intact .
    OUTPUT:
    
Large hiatal hernia . Otherwise unremarkable .