With understanding the biochemical and molecular characteristics of mitochondrial disorders, several point mutations or deficient of mitochondrial DNA have been identified in patients with mitochondrial dysfunction. The clinical manifestations of this disorders are heterogeneous and most patients show abnormality of the central nervous system, skeletal muscle, heart, kidney or these combinations. Especially, cardiac involvement is very important because it is determinant factor for the prognosis. There are two types of cardiac manifestation; cardiomyopathy and cardiac conduction defects. The former is usually hypertrophic, but dilated forms have been demonstrated. The latter is well known as one of three main symptoms in Kearn-Sayre syndrome. We discuss the pathogenesis, pathology and clinical manifestation of mitochondrial cardiomyopathy.