Primary Cardiac leiomyosarcoma is a very rare condition. The authors report the case of a 64 year old woman admitted to hospital for suspected pulmonary embolism, confirmed by thoracic angio-CT scan. Despite thrombolytic therapy, a persistent poor haemodynamic condition associated with a superior vena cava syndrome led to a transoesophageal echocardiographic examination which demonstrated an abnormal intra-right atrial mass obstructing the tricuspid valve. At surgery, a leio-myosarcoma was successfully resected under good conditions. During systematic three-monthly clinical and echocardiographic follow-up, transoesophageal echocardiography detected an asymptomatic local recurrence at 15 months, for which surgery was repeated with adjuvant chemotherapy.