Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The patient is status post coronary artery bypass graft surgery . The heart is again mild - to - moderately enlarged . The mediastinal and hilar contours appear unchanged . The lung volumes are low . There are again patchy opacities in both lower lungs , more extensive in the left lower lobe than right but considerably improved . It is difficult to exclude small persistent effusions but these are markedly improved . Bony structures are unremarkable .
    OUTPUT:
    
Improving pleural effusions and basilar opacities with persistent but decreased left lower lobe opacity . Although superimposed infection is difficult to exclude , the appearance could be explained by atelectasis , scarring , potentially with residual loculated effusion .