A 44-year-old man underwent radical thymectomy for malignant thymoma 5 years ago. He subsequently underwent right extrapleural pneumonectomy because a right pleural metastatic lesion had developed. The operation was completed uneventfully. Immediately after arrival at the intensive care unit, the patient appeared restless and in pain. His heart rate increased to 140 bpm and then abruptly decreased to 20-30 bpm concomitant with profound systolic hypotension of 30-40 mmHg. Chest X-ray showed that the heart was shifted into the right thorax. Emergent re-thoracotomy was performed and the heart was found to be malrotated and herniated from an upper defect of the pericardial patch in the right thoracic cavity. The heart was returned to the pericardium and the defect was covered with a pericardial patch. The blood pressure and heart rate became stable. He was transferred to the surgical ward from the intensive care unit on the first postoperative day. The rest of the course was uneventful and the patient was discharged on the seventh postoperative day. The incidence of cardiac herniation after extrapleural pneumonectomy following chemotherapy for malignant pleural mesothelioma has been reported to be around 3%. The risk of cardiac herniation should always be considered, especially after extrapleural pneumonectomy.