Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Median sternotomy wires are intact . A tracheostomy tube is noted . In comparison to the prior radiograph on ___ , lung volumes are lower . Dense left retrocardiac opacity has slightly improved , and likely represents atelectasis . There is no other focal consolidation . Small pleural effusion on the left . No right pleural effusion . There is no evidence of pneumothorax .
    OUTPUT:
    
Probable left retrocardiac atelectasis , slightly improved performed ___ .