A 29-year-old man presented to the accident and emergency department complaining of a sudden onset of chest and upper abdominal pain. He had a past history of intravenous drug abuse and a previous stab wound to the left hypochondrium that had required laparotomy. On arrival he was distressed with grunting respiration. Initial chest X-ray showed a pneumopericardium. Despite titrated doses of opiate analgesia he became increasingly distressed, agitated and dyspnoeic. Repeat chest X-ray demonstrated an increase in the volume of air present within the pericardial sac. His clinical condition improved rapidly after needle pericardiocentesis decompression. A water-soluble contrast swallow revealed a diaphragmatic hernia with a filling defect in the greater curve of the stomach and contrast medium entering the pericardial sac. A thoraco-abdominal laparotomy confirmed a pre-existing diaphragmatic defect from the previous stab wound, with surrounding adhesions. A small portion of the stomach had herniated through this defect with a perforated gastric ulcer communicating directly into the pericardial sac.