Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart appears at least mildly enlarged . Lung volumes are low . Within the limitations of technique , the mediastinal and hilar contours are otherwise unremarkable aside from noting calcification along the aortic arch . Subpulmonic pleural effusions are difficult to exclude . Chin flexion obscures the left apex . However , aside from suspicion for retrocardiac opacification which would commonly be due to atelectasis , elsewhere the lungs appear clear .
    OUTPUT:
    
Suspected retrocardiac opacity although commonly this would be due to some degree of atelectasis .