Primary cardiac lymphoma, defined as a non-Hodgkin's lymphoma involving only the heart and pericardium, is an extremely rare malignancy. It should be suspected in patients with a heart mass and heart failure, unexplained refractory pericardial effusion or rhythm disturbances. Transvenous intracardiac tumor biopsy under fluoroscopic or transesophageal echocardiographic guidance, is a minimally invasive technique which makes definite diagnosis possible. We describe a patient in whom primary cardiac lymphoma was diagnosed by this technique. He also underwent percutaneous balloon pericardiotomy because of severe refractory pericardial effusion. Seven months after diagnosis and treatment with standard chemotherapy, the patient remained free of disease.