Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The patient is status post median sternotomy and mitral valve replacement . The cardiomediastinal and hilar contours are stable . Chronic upper zone vascular redistribution without overt edema . Lung volumes are low resulting in crowding of bronchovascular structures , particularly at the lung bases . No effusions or pneumothorax .
    OUTPUT:
    
No definite pneumonia . If clinical suspicion persists , a repeat PA radiograph with improved inspiratory level may be helpful for more complete assessment of the lung bases .