Objectives A 28-year-old woman presenting with a 3-month history of dyspnoea after the parturition was referred to our department for the diagnosis of mural thrombus in the left atrium. In the past, she was never found to have heart diseases, lung disease, relevant history of familial heart disorders and she had never been exposure to the poison or radiation during pregnancy. A physical examination revealed a distinct oedema on the face. Routine echocardiography in our centre revealed a huge ‘mural thrombus’ like immobile mass (Figure A,B, asterisks) in the left and right atrium. Subsequent transesophageal echocardiography showed the sessile mass in the atrium, suggestive of malignant tumour, had caused superior vena cava (SVC) and left inferior pulmonary vein obstruction (Figure C,D, arrows; Online Video 1–2). Multidetector CT angiography demonstrated a huge mediastinal neoplasm surrounding the great vessels. The SVC was compressed and invased and it was so narrow (4 mm) that almost no blood could get through (figure E,F). The most common malignancy associated with superior vena cava syndrome is lung cancer, followed by lymphomas and metastatic tumours to the mediastinum. Unfortunately this patient refused to get the surgery for the high medical costs, so the properties of the tumour is unknown, while the case has told us that multimodality imaging is recommended in such a patient in order to distinguish the mural thrombus from the extracardic malignant disorders.