Ultrastructure of cardiac muscle from dystrophic mice

The ultrastructure of cardiac muscle from dystrophic mice was compared with that of their non‐dystrophic littermates. Among the abnormalities observed in the fine structure of the muscle fibers in the dystrophic animals were increased lipid, swollen mitochondria, swollen tubules of the sarcoplasmic reticulum, supercontracted myofibrils, and partially separated intercalated discs. The ventricular muscle appeared to be the region most often affected; in only one of eleven animals did the atrium show discernible effects of the dystrophy. Although a progression of degenerative events seemed to occur, a time schedule could not be determined because of the large variation among hearts of dystrophic animals. The ultrastructure of the hearts from non‐dystrophic littermates was normal. It appears that the depressed cardiac function caused by the myopathy may play a major role in the early death of the dystrophic mice, as in the case of dystrophic hamsters and men. Most of the ultrastructural abnormalities observed could be accounted for if there were an elevation of intracellular free Ca ++ concentration.