A 39-year-old woman presented with a right atrial hemangiosarcoma manifesting as cardiac tamponade with complaints of chest discomfort and dyspnea. Transthoracic echocardiography revealed remarkable pericardial effusion and a right atrial mass. Transesophageal echocardiography disclosed the tumor extending into the right atrial cavity. Surgery found the tumor was poorly demarcated, immobile and adhered to the adjacent right atrial wall and septum. The echocardiographic findings correlated well with the surgical and autopsy findings.