Retro cardiac shadow showing air fluid level is seen in:

Hiatus hernia REF: Sutton's radiology, 7' edition volume 1 page 53 "The classic appearance of a hiatus hernia, with a fluid level superimposed on the cardiac shadow on the PA film, is well known. A Bochdalek hernia arise posterolaterally through the pleuroperitoneal canal and is usually congenital, presenting at bih as respiratory distress. Ninety per cent are left sided. The hernia may contain omentum, fat, spleen, kidney and bowel, in which case a gas shadow is seen within the mass. The ipsilateral lung is invariably hypoplastic with detion of the mediastinum away from the side of the hernia"