Although neoplastic involvement of the pericardium is frequently present postmortem, cardiac manifestations before death are uncommon, and cardiac tamponade as the initial presentation of cancer is rare. We are presenting a metastatic pericardial tumor with cardiac tamponade of unknown primary neoplasm. The patient brought to hospital in a state of unconscious. The chest x-ray film showed cardiomegaly with a globular heart shape and right pleural effusion. We underwent an anterior thoracotomy and pericardial window was created. The histopathologic finding of pericardium, pleural and pericardial effusion show a metastatic adenocarcinoma. The patient subsequently received adjuvent radiotherapy and chemotherapy, but he expired on the postoperative 132 day.