Cardiac biopsy in skeletal myopathy: report of a case with myocardial mitochondrial abnormalities.

Transvenous right ventricular endomyocardial biopsy in an 11-yr-old boy with a proximal skeletal myopathy and a cardiomyopathy, has shown a major increase in mitochondrial size and numbers on electron-microscopic morphometry, with formation of unique ring-shaped mitochondria in cardiac muscle cells. The significance of this finding and the use of cardiac biopsy in children are discussed.