Abstract: AIM:To investigate whether mitochondrial DNA(mtDNA) and nuclear DNA(nDNA) damage increase with age in rat hearts and to explore the changes of DNA polymerase γ(Polγ) in rat hearts.METHODS:Total DNA,RNA and proteins of hearts were isolated.Damages of mtDNA and nDNA were examined with quantitative polymerase chain reaction(qPCR) assay combined with EvaGreen.Gene expressions of mRNA and protein in Polγ were detected with real-time polymerase chain reaction(RT-PCR) and Western blot analysis,and the levels of 8-hydroxy-2′-deoxy-guanosine(8-OHdG) in DNA were studied with ELISA assay.RESULTS:Oxidative DNA damage increased,primarily in mtDNA.The amount of 8-OHdG in DNA significantly increased with age and gene expression of mRNA and protein in Polγ decreased with age.CONCLUSION:The gene expression of mRNA and protein in the key BER enzymes decreases with age,which causes a decrease in the repair capability of the mtDNA and the accumulation of mtDNA damage.Increased mtDNA damage and decreased expression of BER enzymes may cause a "vicious cycle" of oxidative stress that contributes to the accumulation of mtDNA mutations and age-related cardiofailure pathogenesis.