Lymphangioma is a very rare primary tumor of the heart. It is usually incidentally found during autopsies and there have only been a handful of documented cases of this tumor in the heart. In 5 cases, it was discovered accidentally and the remaining cases gave clinical symptoms. Major symptoms of heart lymphangiomas include compression of surrounding mediastinal structures and/or inadequate blood flow through the heart. Specifically the cardiac disturbances lead to rhythm and circulatory failure. The most useful diagnostic tests for this heart tumor include echocardiography, which shows not only the tumor but also its hemodynamic effects. The following article presents the accidental finding of a lymphangioma, localized in the right atrium. It caused considerable difficulty for the blood flow into the right heart chamber, which then led to circulatory failure. In addition we will also discuss all known cases of cardiac lymphangiomas.