[first paragraph of article]Histopathology in patients with HCM is characterized by disarray of the overall architecture of the hypertrophied myocytes, which appear branched and may be intermingled with a variable amount of interstitial fibrosis. These changes may be patched and must be distinguished from the non-specific physiological disarrangement of the junctional area of the septum and the apex. The myocardial cell diameter is another important indicator of hypertrophy. Under normal conditions it ranges from 5–12 μm in diameter. Anything up to 20 μm may be indicative of mild hypertrophy. In moderate hypertrophy cardiocyte diameter is up to 25 μm and moderate to severe hypertrophy is usually between 25-30 μm. For diameters greater than 30 μm severe hypertrophy must be suspected.