We report the case of a patient presenting a sarcoma of interatrial septum with an accelerated growth and a fulminate clinical course documented by non-invasive image diagnostic techniques, habitual in the cardiologic practice. The natural history of some cardiac malignant tumours, as aggressive as in this case, explains the diagnostic delay, the difficulty to establish a curative treatment such as surgery and/or chemotherapy/radiotherapy and the awful short-term prognosis.