Background <p>Multiple myeloma is a malignant plasma cell disorder primarily involving the bone marrow and skeleton, leading to anemia, renal dysfunction, and lytic bone lesions. Extramedullary disease, seen in about 9% of cases, reflects aggressive disease biology with poor prognosis. Common sites include the pleura, liver, and gastrointestinal tract, while pericardial involvement is exceedingly rare and often detected postmortem. Fewer than 25 cases of pericardial effusion or cardiac tamponade due to multiple myeloma have been reported, usually in advanced disease. The mechanism likely involves hematogenous spread or direct extension from adjacent lesions, often associated with high-risk cytogenetic abnormalities. This case presents an unusual first manifestation of multiple myeloma as pericardial effusion with tamponade physiology, emphasizing the need to consider hematologic malignancy in unexplained pericardial effusion, especially in resource-limited settings.</p> Case presentation <p>A 60-year-old Ethiopian man presented with a 6-month history of progressive dry cough, dull chest pain, and worsening shortness of breath. He had been repeatedly treated for pneumonia and pulmonary tuberculosis without improvement. Chest computed tomography revealed a large pericardial effusion with features of cardiac tamponade. Echocardiography confirmed pericardial fluid causing right atrial and ventricular collapse. Pericardiocentesis drained 800&#xa0;mL of hemorrhagic fluid, and cytology showed atypical plasma cells. Further evaluation, including serum protein electrophoresis and bone marrow biopsy, confirmed multiple myeloma. The patient was managed with Pericardiocentesis and systemic chemotherapy, showing clinical and radiologic improvement, highlighting the rarity of pericardial involvement as an initial presentation of multiple myeloma.</p> Conclusion <p>Pericardial involvement in multiple myeloma is an extremely rare and serious manifestation, usually signifying advanced or aggressive disease. While malignant pericardial effusions are commonly due to solid tumors, multiple myeloma should also be considered when no other cause is identified. Early echocardiography-guided pericardiocentesis is lifesaving, and definitive procedures such as a pericardial window may prevent recurrence. This case highlights the importance of suspecting hematologic malignancy in patients with unexplained pericardial effusion or cardiac tamponade. Early recognition and prompt initiation of systemic therapy can improve survival, particularly in resource-limited settings where diagnostic challenges are common.</p>