Rhabdomyosarcoma accounts for 20% of primary malignant cardiac tumours. We describe a woman with cardiac rhabdomyosarcoma. She had loss of appetite, loss of weight, and symptoms of heart failure. A mobile tumour in the left atrium, entering the left ventricle during diastole, was detected by transthoracic echocardiography. The tumour was removed surgically in total; histological diagnosis was rhabdomyosarcoma; however, the patient died after 6 months. In conclusion, primary malignant cardiac tumours can simulate heart failure or systemic disorders. Cardiac rhabdomyosarcomas have a poor prognosis with average survival of 6 months after diagnosis.