Abstract: A 34-year-old woman presented with tamponade and right pleural effusion. After drainage of pericardial and pleural fluid, Computed Tomography (CT) angio was done and massive effusion in lateral of Right Atrium (RA) was reported, but Transesophageal Echocardiography (TEE) revealed large intrapericardial mass with pressure effect on RA and Right Ventricle (RV), so thoracotomy was done and malignant carcinoma of thymus was reported. Malignant carcinoma of thymus has unusual presentations and cardiac involvement as first presentation is uncommon and should be considered.TEE has important role in recognizing and defining tumor.