Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Single upright frontal view of the chest . A pacer is seen overlying the left chest with intact leads in appropriate positions . The lungs are low in volume . There is a patchy opacity at the left lung base suggestive of atelectasis , although pneumonia or aspiration can not be excluded . There is no pleural effusion or pneumothorax . The cardiomediastinal silhouette is stably enlarged .
    OUTPUT:
    
Left basilar patchy opacity most consistent with atelectasis . Clinical correlation is advised .