Ultrastructure of the myocardial fibroma.

The ultrastructure of a myocardial tumor, referred to by a variety of names, which most currently is myocardial fibroma, has been studied. Although the tumor cells did not have the structure associated with protein synthesizing cells or active fibroblasts, there was evidence that they were participating in formation of the abundant stroma rich in collagen and elastic fibers in varying stages of maturity. The morphology of the stromal elements was similar to that in the surrounding myocardium and that described in the "normal" heart but differed from the elastica described in fibroelastosis.