Primary cardiac lymphoma is extremely rare. We present the case of a 70-year-old man with primary cardiac lymphoma involving interatrial septum, presenting as atrial flutter and total heart block. The diagnosis was obtained by echocardiography-guided transvenous endocardial biopsy which revealed diffuse large B-cell non-Hodgkin's lymphoma, CD 20+. After six courses of immunochemotherapy the patient achieved complete remission. After 2 months he developed a series of epileptic attacks. Intracerebral lymphoma extension was diagnosed. Two cycles of high-dose methotrexate and cranial irradiation were applied, resulting in a second complete remission.