A 37-year-old male presented in March 2007 with facial oedema. Quincke oedema was suspected and the patient was treated with parenteral corticosteroids and antihistamines. In spite of the therapy, his condition deteriorated. He developed breathing difficulties and cyanosis of his earlobes. Blood gas analysis showed mild hypoxemia and hypocapnia. A thoracic computed tomography (CT) scan showed collateral circulation and a large mass in the right atrium, extending into and obstructing the superior vena cava. The patient was referred urgently to the Cardiosurgery Department, where the tumour was partially resected. It was 50 × 50 × 40 mm in size, weighed 46 g and was covered with an incomplete thin, fibrous, elastic, solid light-brown to greenish membrane. It contained two dark-brown thrombotic masses, 30 × 15 × 10 mm and 25 × 18 × 8 mm in size. Microscopy of the tumour showed blast-like cells with round, irregular or elongated nuclei, finely granulated chromatin, large nucleoli and scanty basophilic cytoplasm. Mitotic and apoptotic indexes were high. There were numerous macrophages involved in phagocytosis of apoptotic debris, creating a ‘starry sky’ appearance. Immunohistochemical analysis showed cells clearly positive for CD45, CD34, CD117 and myeloperoxidase. Cells were negative for epithelial membrane antigen, cytokeratin, vimentin, S100, neurone-specific enolase, chromogranin A, synaptophysin, desmin, Myo D1, CD99, terminal deoxynucleotidyl transferase, CD15, CD68, lysozyme, CD31, CD79a, CD20, CD10, CD1a, CD3, CD4, CD5, CD7, CD8, CD43, CD45RO, CD56, CD57, CD30 and ALK-1. Proliferative activity was high (up to 40% of cells were Ki67+). A diagnosis of extramedullary myeloblast proliferation without maturation (myeloid sarcoma) was made. The patient was then admitted to our institute for further tests. Morphology and flow cytometry did not show any leukaemic infiltration of the bone marrow. Repeated CT scanning showed the right atrium to be completely filled with a solid, avascular tumour mass, with irregular contours, measuring 44 × 67 × 82 mm (top left), that did not spread into the right ventricle or left side of the heart (top right). There was a well-developed collateral circulation (bottom) between the inferior vena cava and the jugular vein. Combination chemotherapy with daunorubicin and cytarabine was commenced.