Background: There are some reports in the literature, which suggest that cardiac tamponade drainage may transiently affect systolic function and also cause acute respiratory distress syndrome (ARDS). We did not find any reports of acute ventricular failure and ARDS secondary to mediastinal tumor resection without tamponade. Case Report: Here we report a 48-year-old woman presenting with massive pericardial effusion without tamponade in whom tumor was resected through median sternotomy using cardiopulmonary bypass. ARDS and acute heart failure were two rare complications that happened at the end of the operation secondary to a sudden decompression of the heart from tumor pressure. Conclusion: ARDS and acute heart failure are two rare complications, which can happen after large mediastinal tumor resection.