Primary pediatric heart tumors are rare, and the vast majority are benign. Primary malignant cardiac tumors are exceedingly uncommon in this age group. Due to their rarity and overlapping imaging features with the more common benign tumors, the diagnosis of primary malignant cardiac tumors is particularly challenging. We report a case of a 12-year-old male with a 7-year history of a left ventricular mass that progressively increased in size, eventually requiring surgical resection. The histological diagnosis was a myoepithelial carcinoma with an EWSR1::KLF15 fusion. Consistent with previously reported tumors harboring this fusion, a poorly differentiated small cell component was observed. Adjuvant chemotherapy comprising four cycles of ICpE and one cycle of IVE. At 11 months after completion of chemotherapy, there is no evidence of recurrent or metastatic disease.