Liposarcoma originating in the heart is extraordinarily rare. Herein, we report a dedifferentiated liposarcoma arising from the left atrium in a 59-year-old Chinese man. Histologically, the neoplasm predominantly consisted of undifferentiated pleomorphic sarcoma. In addition, the neoplasm exhibited lipoblastic differentiation and osteo-/chondrosarcomatous components. Immunohistochemically, the neoplastic cells were strongly positive for p16, MDM2, and CDK4. Fluorescence in situ hybridization showed MDM2 gene amplification in all of the tumor components. To the best of our knowledge, this is the first published example of cardiac dedifferentiated liposarcoma exhibiting homologous and heterologous differentiation without a well-differentiated liposarcoma component.