Primary tumors of the cardiac valves are rare. One of the most common reasons that left-sided cardiac tumors come to clinical attention is embolization to the systemic circulation. We present two children who suffered left coronary arterial occlusion due to embolization of a sarcoma of the mitral valve. A 6-year-old female who had been admitted to the hospital after cerebrovascular embolization of a fragment of sarcoma of the mitral valve experienced sudden cardiovascular collapse due to occlusion of the left coronary artery. She was placed on extracorporeal membrane oxygenation, and underwent coronary embolectomy and resection of the tumor from the mitral valve and its tendinous cords. Left ventricular function did not improve, and she underwent orthotopic heart transplantation. On follow-up 32 months after transplant, the patient is well, with no evidence of recurrence of or metastasis from the tumor. The tumor arose from the leaflets and tendinous cords of the mitral valve, and was composed grossly of multiple white nodules. Histopathologic evaluation disclosed fragments composed predominantly of peripheral spindle cells in an extensive fibromyxoid stroma. The mildly pleomorphic cells of the tumor gradually blended with adjacent pieces of the mitral valvar leaflet and tendinous cords. Immunohistochemical studies revealed strong staining for vimentin, smooth muscle actin, muscle specific actin, and myoglobin, suggesting myogenic differentiation. The other patient was a 2½-year-old female who died suddenly at home. Grossly and histologically, the tumor was essentially identical to the first case, and there was a 3 cm string-like extension passing into the orifice of the left coronary artery. To put the cases in context, we compare them with other descriptions of this rare type of tumor.