Primary malignant heart tumors represent rare entities where fibro sarcoma represents about 3% of all. Introducing the patient: A 15 years old patient with cardiac insufficiency (heart failure) symptoms, such as weakness, cyanosis, palpitations and breathing difficulties; enlargement of upper mediastinum and pleural effusion. Through echocardiography a pericardial effusion and intracavitary thrombus in atrium was diagnosed. With computed tomography is diagnosed a tumoral mass in right atrium which is also spread in the right ventricle of the heart. Tumor is completely removed; pat histology result showed primary fibro sarcoma of the heart. At that time no metastasis was found. Conclusion. Primary malignant heart tumors may manifest like cardiac insufficiency or like systemic diseases. Fibrosarcomas are rare and have bad prognosis. On average patients can live around six months after initial symptoms appeared and diagnosis of the tumor was done. In the case of cardiac insufficiency with differential diagnosis we should also think of heart tumors, which could certainly be proved for or eliminated by echocardiography.