Rearrangements of JAZF1 are a frequent genetic aberration in endometrial stromal tumors. We report a distinct primary cardiac ossifying sarcoma that harbored a JAZF1/PHF1 fusion. The patient was a 70-year-old man with a history of a 6.8 cm calcific intramural left ventricular mass. Six years after his initial evaluation, the patient developed multiple lung metastases and ultimately died of disease-related complications. Histologically, the cardiac tumor and lung metastases demonstrated an infiltrative, malignant spindle cell neoplasm that grew in short fascicles with areas of bone formation, nuclear palisading, and necrosis. The neoplastic cells were relatively monomorphic in a background of an amorphous collagenous matrix. Immunohistochemical analysis was positive for vimentin and negative for wide-spectrum cytokeratins, S100 protein, desmin, smooth muscle actin, and CD34. Fluorescence in situ hybridization using a dual-color, single-fusion probe set identified the JAZF1/PHF1 fusion. The unique morphology and the presence of a JAZF1/PHF1 rearrangement suggest that this distinctive ossifying sarcoma is not part of a currently established diagnostic entity, representing instead a novel primary cardiac sarcoma. This case also represents the first description of a JAZF1 fusion in a tumor outside the spectrum of endometrial stromal neoplasms.