Variations in microscopic anatomy and ultrastructure of human embryonic hearts subjected to three different modes of fixation.

The external form and the internal contour of the ventricular surfaces were studied in human embryonic hearts following three modes of fixation: A) simple immersion fixation, B) indirect ventricular perfusion through the umbilical vein and C) high flow-low pressure ventricular perfusion-inflation. Fixation artifacts, resulting in distortion of the external form of the heart together with distortion of the internal contour of the ventricular cavities, were observed in specimens submitted to modes A and B of fixation. By contrast, hearts fixed by direct ventricular perfusion-inflation (C), showed less distortion in their external form, and the various intraventricular components maintained their spatial relationship among themselves and with the great arteries. Thus, reproducible developmental anatomical features at organ and tissue levels were readily available for study. The relevance of a direct ventricular perfusion-fixation method is discussed in relation to the value of human cardiac developmental data obtained in the past, after using simple immersion, or other modes of fixation.