Sternal fracture is relatively common in chest trauma. Mediastinal hematoma secondary to sternal fracture is not in common, and it has minor symptoms such as mild dyspnea and chest tightness, which usually resolve spontaneously. We experienced two cases of extrapericardial tamponade by hematoma caused by sternal fractures. Two patients were diagnosed by chest CT scan and sent to the operating room within 2 hours after arriving at emergency room because of unstable vital signs. Cardiovascular signs were relieved immediatly after the operation. We report these cases with a brief review of the literature.