A 73-year-old man had myocardial infarct and coronary emboli from a left atrial myxoma diagnosed at necropsy. The tumor was attached to the atrial roof and showed no local myocardial infiltration. Transmission electron microscopic (TEM), light microscopic, and immunoperoxidase (IPX) studies confirmed the neoplastic character of this lesion and pointed to undifferentiated mesenchymal cells as the origin of the atrial myxoma cells. This case emphasizes two aspects: (1) glandlike structures were also found in the myxoma, and their epithelial-like nature was supported by TEM and IPX studies, which showed positivity for carcinoembryonic antigen and H blood substance; (2) many systemic tumor masses were found, and their metastatic nature was evidenced by the markedly infiltrative and destructive character; the only cytologic marker that could discriminate this case from other usual, noninfiltrative cardiac myxomas was the epithelial-like cells.