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Rosai-Dorfman disease (RDD), also known as sinus histiocytosis with massive lymphadenopathy, is a nonmalignant disease of unknown etiology. It may present as bilateral, massive, painless cervical lymphadenopathy; however, one third of the cases have extranodal involvement. Extranodal sites include soft tissue, skin, upper respiratory and gastrointestinal tracts, and central nervous system, with head and neck being the most common. Here we report a rare case of intracardiac RDD in a 46-year-old, African-American female who presented with worsening shortness of breath and fatigue for 7 weeks. Comprehensive physical examination was within normal limits; the patient had no lymphadenopathy. Echocardiogram revealed a large mass in the left atrium extending into the mitral valve. The mass was resected under the pretext of clinical diagnosis of myxoma, and the patient underwent a radical extended interatrial septectomy with bovine pericardial patch reconstruction. The 8-cm resected mass consisted of areas of fibrosis alternating with sheets of histiocytes enmeshed in a mixed inflammatory infiltrate. Histiocytes contained intact lymphocytes, plasma cells, neutrophils, and erythrocytes suggesting emperipolesis. The diagnosis of RDD was confirmed by immunohistochemistry. This case highlights the extranodal manifestation of RDD in the heart which could be easily mistaken for a myxoma on clinical and radiologic evaluation. RDD must be considered in the differential diagnosis of any patient who presents with a cardiac mass.