Primary pericardial malignant mesothelioma is a very rare clinical entity and its prognosis is very poor. We herein report a 67-year-old man who presented with pericardial mesothelioma that was diagnosed 21 months after the onset of cardiac tamponade as the initial manifestation. Despite undergoing pericardiocentesis and surgical pericardial fenestration at the onset of cardiac tamponade, we were unable to make a conclusive diagnosis of mesothelioma based on the cytological and histological findings. This unusual case had a relatively long progression-free period without treatment before the appearance of pleural tumors that showed the histological features of malignant sarcomatoid mesothelioma.