Primary cardiac lymphoma as a cause for pericardial effusion and cardiac tamponade is uncommon in dogs. Diagnosis and treatment of cardiac lymphoma is challenging, with guarded prognosis. A German shepherd dog was presented with an enlarged abdomen, reduced appetite, dyspnoea and nocturnal coughing. Pulsus paradoxus, hyporesonant thorax, ascites, hepato and splenomegaly were found in examination. Normal complete blood count, elevated blood urea nitrogen and albumin levels in biochemical panel and microfilaria in blood were identified. Pleural effusion, pulmonary edema and cardiomegaly in thoracic radiography, ascites in abdominal ultrasonography, pleural effusion, fibrinous adhesions, severe pericardial effusion with cardiac tamponade in echocardiography were identified. Also, free-floating structures, hypoechoic masses were seen adhered to the myocardium, pericardium and base of the aorta in echocardiography. Pericardial fluid analysis identified Dirofilaria repens microfilaria and lymphoma cells. Levemisole was given to eliminate microfilaria and a modified COP chemotherapy protocol consisting cyclophosphamide, vincristine and prednisolone was initiated against the lypmphoma. By day 3 of levamisole treatment, microfilaria in blood and in pericardial effusion was negative and by week 3 of chemotherapy, pericardial effusion and lymphoma were absent. Meanwhile, the patient developed Babesia gibsoni infection and immune mediated hemolytic anemia, treated with imidocarb dipropionate. A day after the week 4 of chemotherapy, sudden dyspnoea and pleural effusion were developed and the patient succumbed. The clients had a lapse in the oral chemotherapy during the last week. Chemotherapy is effective against cardiac lymphoma but the schedule must strictly be adhered. Concurrent hemoparasitism and immune mediated conditions may complicate the clinical outcome of primary cardiac lymphoma. 1546248299.php