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Figure 2 Ventricular septal tissue sections from a normal control, age 36 years (A and B) and a 31-year-old patient with HCM who died suddenly (C–F). All sections are stained with picrosirius red and viewed at the same magnification (x400) using standard light (left panels) or polarization (right panels) microscopy. A and B: Structurally normal heart. Thin collagen fibers are stained red (A) and appear green-to-yellow under polarized light (B). Various components of the normal collagen matrix are visualized consisting of the perimysial coils (solid arrows), pericellular weaves (open arrows) and intercellular struts (triangles). C and D: HCM in an area of normally arranged and longitudinally sectioned cardiac muscle cells. All components of the collagen matrix are increased in amount and differ morphologically from controls. The perimysial coils (solid arrows) are thickened and appear to be stretched (reduced degree of coiling). Pericellular weaves (open arrows) and struts (triangles) are abundant and thickened. E and F: HCM in an area of disorganized cardiac muscle cells. Perimysial coils (solid arrows), pericellular weaves (open arrows) and struts (triangles) are significantly increased in amount and are also arranged in a markedly disorganized pattern.