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Figure 3 Histopathology of the tissue membranes constituting a patent foramen ovale. (a) Longitudinal section of the atrial septum, showing a patent foramen ovale (box) with valve (arrow). The superior epicardial surface (E) and a portion of the mitral valve (MV) are also seen. The septal wall consists predominantly of myocardium and adipose tissue. RA = right atrium. (b) A higher magnification of boxed area in panel a, showing the valve with a thickened fibrotic right endocardial surface (arrow). The atrial septum (*) in this region consists of myocardium and becomes predominantly fibrotic inferiorly. Movat x1.25. (c) A higher magnification of the valve from the left side, showing a relatively thin endocardial surface (arrow). The underlying myocardium is composed of bundles of cardiac myocytes. Movat x20. (d) A higher magnification of the valve from the opposite side (right), highlighting the endocardial surface (arrow), which consists of a thick layer of collagen and elastic fibers. Movat x20.
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