Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Dual lead left - sided pacemaker is again seen with leads extending to the expected positions of the right atrium and right ventricle . The patient is status post median sternotomy and cardiac valve replacement . Retrocardiac opacity is again seen consistent with a large hiatal hernia . There is mild bibasilar atelectasis . Very trace pleural effusion would be difficult to exclude , although no large pleural effusion is seen . There is no pneumothorax . The cardiac and mediastinal silhouettes are stable .
    OUTPUT:
    
Large hiatal hernia and bibasilar atelectasis . While very trace pleural effusion would be difficult to exclude , no large pleural effusion is seen .