Background Primary cardiac tumors are extremely rare with an autopsy incidence of 0.05%. They can present with a variety of symptoms, including life threatening arrhythmia and cardiac tamponade. In this case report, we focus on the diagnostic process and management of a primary cardiac lymphoma presenting with cardiac tamponade. Case summary We report on a 71-year-old male presenting with a large pericardial effusion, tamponade, and a mass in the right atrioventricular groove. Multimodality imaging was performed, including transthoracic echocardiography, computed tomography, magnetic resonance imaging, positron emission tomography and computed tomography-guided transthoracic biopsy The final diagnosis of a double-hit diffuse large cell B-cell lymphoma was made, for which treatment consisting of a combination of chemotherapy and immunotherapy was initiated. Low-dose colchicine was also added to the treatment. Discussion Primary cardiac lymphoma remains a very rare diagnosis and this case highlights the need for multimodality imaging and imaging-guided biopsy to differentiate cardiac masses. First-line treatment for primary cardiac lymphoma remains a combination of chemotherapy with immunotherapy, with addition of low-dose colchicine to prevent recurrence of malignant pericardial effusion.