Primary malignant cardiac tumours are extremely rare. They count for a quarter of all possible cardiac tumors, and are mostly sarcomas. For a long time, their diagnosis was made post mortem, and they were only reported through autopsy series. Since then, diagnostic and therapeutic advances have been made, making clinical diagnosis of this entity more accessible ante mortem. Nevertheless, due to their rarity, cardiac sarcomas suffer from a lack of therapeutic guidelines. Their treatment is modelled on that of sarcomas developed in other organs of the body. We report an interesting case of a 74-year-old female patient operated on for an infiltrating sarcomatous tumour of the left atrium revealed by dyspnoea associated with cardiac palpitations. Thoracic angioscan and transthoracic echocardiography led to the diagnosis of a cardiac tumour, and the thoracic-abdominal-pelvic Computed Tomography (CT) scan did not reveal any other extracardiac lesions except for a minimal non-neoplastic bilateral pleural effusion. The patient underwent an incomplete surgical procedure with R2 resection followed by adjuvant chemotherapy with doxorubicin monotherapy. The evolution under this treatment was marked by a locoregional progression of the disease with further progression in the atria, mediastinum and dorsal spine after 4 courses. A second line of chemotherapy with Dacarbazine monotherapy was initiated, but the patient died shortly after receiving two courses of the new treatment.