Malignant non Hodgkin’s lymphomas are rare in the absence of human immunodeficiency virus infection and it is exceptional for a cardiac site to be the prominent feature. In our case, the malignant lymphoma was revealed by dyspnea, pericardial effusion in a context of alteration of the general state. Transthoracic and transesophageal echocardiography revealed in the right atrium, a solid lobulated mass arising from the right atrial wall. There was a thickness of the interatrial, interventricular septum and the anterior mitral leaflet attachment site on the left atrial wall. Magnetic resonance imaging showed a a 3x3 cm. of dimension mass on the right atrial posterior wall at the proximity of the superior vena cava. After sternotomy and direct biopsy, histopathological and immunohistochemical diagnosis was large B cell high grade lymphoblastic non Hodgkin’s lymphoma. The patient died 7 months after the diagnosis despite polichemotherapy and radiotherapy because of the central nervous system invasion. The regression of the cardiac tumor was checked by transthoracic echocardiography during the treatment. The patient had a relatively short time of partial remisson of 3 to 4 months duration.