There is a difference between pleural effusion and pericardial effusion, first of all in terms of their location. Pleural effusion occurs in the chest cavity, while pericardial effusion occurs in the pericardium. The two can be differentiated by imaging. A pleural effusion appears as an arcuate band of fluid density in one or both thoracic cavities, and when the amount of fluid is large, there can be incomplete expansion of lung tissue or atelectasis on one side. Pericardial effusion is characterized by fluid density shadows in the pericardium. Patients with small amount of pericardial effusion have no clinical manifestations, while patients with large amount of pleural effusion may show dyspnea and chest tightness.