A 5 year old boy with acute ly mphoblastic leukaemia on chemotherapy presented with chest pain and vomiting for two days after an elective procedure under general anaesthesia. H is ches t x-ray was remarkabl e for a promin ent halo sign, an air gap surrounding the he art indicat ing a large pneumope ricardium. Alth ough the pneu mo pericardium could not be appre ciated on an echocardiogram, the child developed clinical sig ns of cardiac t amponade. Attem pts to evacu ate the pneumopericardium were unsuccessful leading to death.