Seven cardiac myxomas (CM) were studied by light and electron microscopy (EM) and their features compared with previously reported CM. Tumor cells were enmeshed within abundant stroma composed of fine electron dense granules. These cells were present either singly or more often in closely apposed small groups. The most distinctive ultrastructural feature in all seven CM was the presence of numerous cytoplasmic filaments. Our findings did not support a distinct separation into multiple cell types that could be clearly classified since the tumor cells had combined features of smooth muscle cells and fibroblasts. There has been no agreement on the principal cell type observed in CM, which has resulted in numerous theories about their histogenesis. Although the cell of origin of CM remains elusive, we fell that CM arise from primitive mesenchymal cells with multipotential capabilities for cell differentiation. Evidence is presented supporting the fact that CM are neoplasms and not thrombi. CM rarely recur but no bona fide metastasis has been reported.