This paper presents the case of a 35 year-old woman with symptoms of heart failure from the last month. A physical examination at admission showed paleness, dyspnea, peripheral edema and fatigue. In a two-dimensional echocardiography and transesophageal echocardiography, normal thickness but severe left and right ventricular dysfunction with severe pericardial effusion and thickened pericardium were found. In the enlarged right atrium, an oval-shaped structure was found with features of continuity with lateral right atrial wall and also a bulging of the structure through the orifice of the tricuspid valve to the right ventricle. In the echocardiography, we did not saw any blocking of the tricuspid valve or the inflow from inferior vena cava (IVC) or superior vena cava (SVC) or coronary sinus. On the basis of the echocardiography examination and clinical presentation, tentative diagnosis of the right atrium myxoma was made. A coronary angiography revealed normal coronary arteries and no feeding of tumor by branch of right coronary artery (RCA). Surgical removal of the tumor was performed without complication. The histopathological examination confirmed the diagnosis of angiosarcoma. In the follow-up echocardiography carried out after three months, severe left ventricular (LV) and right ventricular (RV) dysfunction continued and was demonstrated. Magnetic resonance imaging revealed no lymphadenopathy or re-growth of the tumor in the mediastinum or pericardium.