Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Mitral valve prosthesis is noted . The sternotomy wires are unchanged . The lungs are clear , but hyperinflated , compatible with known emphysema . Cardiomediastinal silhouette is mildly enlarged , unchanged . There is no evidence of pneumonia or congestive heart failure . A small hiatal hernia is present .
    OUTPUT:
    
No evidence of acute intrathoracic process .