Ultrastructural examination of the LV myocardium revealed focal cardiomyocyte remodeling characterized by normal areas interspersed with sections of sarcomeric disorganization and mitochondrial abnormalities. WD feeding caused swollen mitochondria with loss of mitochondrial matrix electron density, loss of cristae and mitochondrial fragmentation (Fig. 3, left panel). Daily exercise prevented the focal cardiomyocyte remodeling. WD fed mice treated with exercise also showed normal sarcomeric arrangement. There was no mitochondrial swelling in exercising WD fed mice and the mitochondria retained their normal electron dense structure with exercise (Fig. 3, right panel).