This is image is a mosaic of several images showing the full thickness of
the wall of the heart of a rat. The myocardium, composed of cardiac muscle
cells with supporting blood vessels, makes up most of the wall. The edge in
the upper part of the image is covered by a thin endocardium, which lines
the lumen of the heart, whereas the edge in the lower part of the image is
the outer surface of the heart, covered by the epicardium.
