In the patients with mitochondrial cardiomyopathy, fragmentation and oxidative damage in mtDNA was documented at their age 7 to 19 equivalent to the normal subjects of age over 80.Exposure of a cultured cell line under oxygen stress, 95% oxygen, cold mimic these changes in mtDNA 1within 3 days leading as apoptotic cell death, whereas mtDNA lacking cells are relatively immune.These facts support the 'redox mechanism of agening'.