Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP upright and lateral chest radiographs were obtained . The lungs are well expanded and clear with the exception of retrocardiac faint opacity which is most likely atelectasis . There is no pleural effusion or pneumothorax . subtle gas lucency projecting over the heart at the midline could represent air in the distal esophagus or a subtle hiatal hernia . The heart is normal in size with normal cardiomediastinal contours . No displaced rib fractures are identified .
    OUTPUT:
    
No acute intrathoracic process .