Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The patient is status post previous median sternotomy and coronary artery bypass surgery . Heart size is normal , and mediastinal contours are stable in appearance . Previously present linear focus of atelectasis in the left lower lobe has resolved and the left pleural effusion is no longer apparent . On the lateral radiograph , subtle peribronchial opacities are present in the retrocardiac region and likely correspond to the left lower lobe on the frontal view . Lungs and pleural surfaces are otherwise clear . Tracheostomy tube remains in place within the trachea .
    OUTPUT:
    
Subtle retrocardiac opacity , which could reflect either atelectasis or developing pneumonia . Followup radiographs may be helpful in this regard .