Abnormal Mitochondrial Appearance in BTHS Dilated Cardiomyopathy. (A) Electron micrograph of cardiac muscle biopsy from a patient with severe BTHS DCM. The myocyte cytoplasm contains increased numbers of mitochondria, most being larger than normal. Lipid is not increased but pools of non-membrane bound glycogen are evident. (B) Higher power electron micrograph. The mitochondria are enlarged and are crowded together, with many touching one another. The cristae are not parallel but are stacked, and many are in abnormal circular arrays (red arrow). The nucleus (starred) is centrally placed, but the myofilaments, with their cross-striations (blue arrows), are displaced to the periphery of the cell. (C) High power photomicrograph of myocardium stained with Masson-Trichrome stain. The myocytes are vacuolated with pale areas around the nucleus. In some giant mitochondria are visible as rounded, red bodies [arrows]. Such giant mitochondria are very suggestive of mitochondrial pathology and reflect the giant mitochondria seen on electron microscopy.