Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Portable AP chest radiograph was obtained . The lungs are low in volume but clear aside from retrocardiac opacity likely residual atelectasis . There is no pleural effusion or pneumothorax identified . The heart is stably enlarged with otherwise normal mediastinal and hilar contours . Dual lead pacemaker is noted .
    OUTPUT:
    
Retrocardiac atelectasis without acute intrathoracic process .