Primary myocardial involvement of Diffuse Large B-Cell lymphoma is extremely rare, accounting for 0.5 % of all lymphomas. We report a 65-year-old male, presenting with an acute cardiac tamponade, which was drained. A pericardial window with myocardial biopsy was carried out, disclosing a diffuse large B cell lymphoma. He received 6 cycles of rituximab, cyclophosphamide, vincristine, and prednisone (R-CVP), without response. Finally, a palliative chemotherapy with gemcitabine plus oxaliplatin was prescribed.