Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: A left pectoral pacemaker is again noted , with leads in standard positioned . Aortic and mitral valve prostheses are present . Status post sternotomy . The heart is mild enlarged but unchanged . There is upper zone redistribution , but no overt CHF . No gross pleural effusion . Retrocardiac opacity is noted . No pneumothorax . Densities , including nodular densities , seen on the ___ chest CT , are not well appreciated radiographically . The previously described partially calcified nodule is faintly visible in the right mid zone laterally .
    OUTPUT:
    
Retrocardiac opacity is presumably atelectasis , however , pneumonia should be considered in the appropriate clinical setting . Densities , including nodular densities , seen on the ___ chest CT , are not well appreciated radiographically .