Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Support Devices : There is an implanted pacemaker with leads in unchanged position . There is increased heterogeneous opacity in the left lower lobe , most apparent on the lateral view . The lungs are otherwise clear . The hilar and cardiomediastinal contours are normal . There is no pneumothorax or pleural effusion . Pulmonary vascularity is normal .
    OUTPUT:
    
Heterogeneous opacity in the left lower lobe likely due to atelectasis but pneumonia or aspiration in the appropriate clinical setting can not be excluded .