Histological and ultrastructural evaluation of cardiac lesions in idiopathic cardiomyopathy in dogs.

Described are pathological studies of eight dogs which died in congestive heart failure, with a clinical diagnosis of congestive cardiomyopathy. Examination revealed marked dilatation and enlargement of all four chambers of the heart. The ventricular walls were thin with small atrophic papillary muscles. Histological studies on the myocardium revealed scattered areas of myocardial necrosis, especially around the papillary muscles of the left ventricle and random scattered areas of fibrosis. Electron microscopic studies revealed fewer and disoriented myofibrils, myocytolysis, increased numbers of mitochondria with swelling and inclusions, increased glycogen granules and increased numbers of lysosomes, lipofuscin granules and lipid droplets. Mild Z-band abnormalities were found throughout the myofibers.