Two cases are reported of cardiac herniation complicating intrapericardial pneumonectomy in the early postoperative period. Both patients had a radical pneumonectomy for right-sided bronchial carcinoma invading, in one patient, the carina and the superior vena cava. The pericardial defect, made necessary by the surgical procedure, had not been closed in either patient. About two hours after the end of surgery, both patients, lying supine, developed a state of shock, with tachycardia and arterial hypotension. The diagnosis of cardiac herniation was made in both cases on the chest film. Placing the patient on his left side was only partly efficient in one patient, slowing the heart rate from 160 b.min-1 to 120 b.min-1 and increasing the systolic blood pressure (from 60 mmHg to 80 mmHg). Both patients therefore required to be operated on again. In one patient, the heart had completely herniated through the pericardial defect, and had turned to the right side about the vena caval axis; in the other patient, partly improved by being turned to his left, the heart had returned to its normal position. The pericardial defects were closed in both cases with a strip of dura mater previously treated with 2 (ethyl-mercurithiol-5-benzoxazol) carboxylic acid. The immediate postoperative course was uneventful. Unexpected symptoms and sign occurring in the early postoperative period after intrapericardial pneumonectomy must imperatively lead to carrying out a chest X-ray.