The clinical presentation of oncological malignancies may vary widely. Herein, we present a patient with a huge mediastinal mass surrounding the heart, which caused the right ventricle to collapse. The mass was diagnosed as T-cell lymphoblastic lymphoma. Treatment consisted of intrathecal prednisone, ARA-C, methotrexate, and the CHOP chemotherapy regimen. Transthoracic echocardiography revealed disappearance of the paracardiac mass in front of the right ventricle at the 2-month follow-up.