Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Dual - chamber pacemaker lead tips are in the right atrium and right ventricle , unchanged since prior examination . Lungs are clear except for a patchy left retrocardiac opacity obscuring the medial left hemidiaphragm and a portion of the descending thoracic aortic interface . No pleural effusion or pneumothorax . Moderate cardiomegaly is stable . Mediastinal contour and hila are otherwise unremarkable .
    OUTPUT:
    
Patchy left retrocardiac opacity could potentially represent an early focus of pneumonia , localized aspiration or atelectasis .