Ultrastructure of the rat papillary muscle-chorda tendineae junction.

The papillary muscle and chordae tendineae of the rat tricuspid valve were treated with tannic acid-glutaraldehyde fixative and examined with an electron microscope. In the junctional region, the papillary muscle cell tapered abruptly and separated into many processes. One end of bundles of elastic fibers approached these processes or lateral sides of the muscle cell and the other end extended in a longitudinal direction toward the chordae tendineae. Fine networks of elastic fibers were observed in the subendothelial layer of the junctional region.