Abstract
A detailed study has been made of the ultrastructure of a cardiac myxoma from a man aged 41 years. It consists of abundant mucoid stroma in which are scattered single or grouped rounded or stellate cells. The stroma consists mainly of finely granular material with scanty fibrin which is seen predominantly on the surface aspect. No formed collagen is found. The myxoma cells contain numerous mitochondria, Golgi complexes and associated vesicles, moderate amounts of rough endoplasmic reticulum and scanty residual bodies. There is little evidence of pinocytosis. They also contain similar granular material to that found in the stroma. We consider, therefore, that the myxoma cells are biosynthetically active and are responsible for the production of the stroma. Morphologically the lesion does not show the features of a thrombus and we consider that it is most probably a neoplasm, although at present there is no evidence as to the cell of origin.