Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The patient is status post recent median sternotomy and aortic valve replacement . Cardiomediastinal contours are stable in appearance in the post-operative period . Slight improvement in degree of left lower lobe atelectasis but unchanged small left pleural effusion . Minimal atelectasis at right lung base and small right pleural effusion are also similar to the prior study . No visible pneumothorax . On the lateral radiograph , an apparent small air - fluid level is present in the upper retrosternal region . This can not be compared to prior studies due to absence of a lateral view on previous exams .
    OUTPUT:
    
1 . Improving left lower lobe atelectasis and persistent small pleural effusions , left greater than right . 2 . Apparent small retrosternal air - fluid level on lateral view , which could reflect post-operative changes in the anterior mediastinum or a small loculated hydropneumothorax .