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 mildly enlarged . The cardiac , mediastinal and hilar contours appear stable . Opacification at the left lung base has substantially improved . A small caliber chest tube at the base of the left hemithorax is not optimally visualized . There is no pneumothorax or pleural effusion .
    OUTPUT:
    
Decreased opacification at the left lung base . Small caliber chest tube visualized at the base of the left chest .