Background: The cardiac mitochondria are the power house of heart cells and are also involved in other important cellular processes including apoptosis, oxidative stress and signaling pathways that are key determinants of the heart’s ability to withstand cardiac insults. Reports have shown that the ageing heart is more vulnerable1 to ischemia/reperfusion (I/R). Whether the mitochondrial proteome of the ageing heart reflects this is not presently known. The aim of this study was to investigate the effect of ageing on cardiac mitochondrial proteins and to establish whether the changes are related to stress and to cardiac vulnerability to I/R. Methods: Cardiac protein extracts from adults (2 months old) (n=4) and from aged (18 months old) (n=5) male C57BL/6 mice were processed using isobaric tandem mass tagging and analyzed by reverse phase nano-LC-MS/MS as described previously2. Mice were killed by a lethal dose of anesthetic (intraperitoneal (IP) injection of 20mg of pentobarbital sodium), and cardiac ventricles were used for protein extraction and quantification as described previously2. Mitochondrial proteins were identified, and statistical analysis (unpaired t-test) was performed to compare protein expression between adult and aged groups. Results: Proteomic analysis yielded 6077 cardiac proteins in total. There were 435 (7%) mitochondrial proteins and only 127 of these proteins displayed a statistically significant (p<0.05) change (increase or decrease) with ageing. The majority (95%) of the mitochondrial proteins that changed with age were significantly upregulated with ageing. In particular there was an upregulation of proteins associated with fatty acid metabolism, TCA cycle intermediates and electron transport (45 proteins). There was also an increase in the expression of two pro-apoptotic proteins (diablo Homolog & Apoptosis-inducing factor 1) with ageing. On the other hand, ageing was associated with a marked downregulation in mitochondrial aldehyde dehydrogenase. Conclusion: This work reports a signifcant remodelling of mitochonrial proteome as a result of ageing. The changes in mitochondrial proteins are consistent with increased stress and vulnerability to cardiac insults as shown by increased lipid metabolic activity, pro-apoptotoic factors and deacrese in aldehyde dehydrogenase expression. Further work is being carried out to determine whether these proteins are altered during I/R.