Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The patient is status post median sternotomy and aortic valve replacement . Heart size is normal . Mediastinal and hilar contours are unchanged . Pulmonary vasculature is not engorged . Patchy opacities in the lung bases likely reflect atelectasis in the setting of low lung volumes . No focal consolidation , pleural effusion or pneumothorax is present . Mild elevation of the left hemidiaphragm appears to be chronic . No acute osseous abnormalities detected .
    OUTPUT:
    
Low lung volumes with mild atelectasis at the lung bases .