Evidence suggests that aging, per se, is a major risk factor for cardiac dysfunction. Oxidative modification of cardiac proteins by non‐enzymatic glycation, i.e. advanced glycation endproducts (AGEs), has been implicated as a causal factor in the aging process. This study was designed to examine the role of aging on cardiomyocyte contractile function, cardiac protein oxidation and oxidative modification. Mechanical properties were evaluated in ventricular myocytes from young (2‐month) and aged (24–26‐month) mice using a MyoCam® system. The mechanical indices evaluated were peak shortening (PS), time‐to‐PS (TPS), time‐to‐90% relengthening (TR90) and maximal velocity of shortening/relengthening (± dL/dt). Oxidative stress and protein damage were evaluated by glutathione and glutathione disulfide (GSH/GSSG) ratio and protein carbonyl content, respectively. Activation of NAD(P)H oxidase was determined by immunoblotting. Aged myocytes displayed a larger cell cross‐sectional area, prolonged TR90, and normal PS, ± dL/dt and TPS compared with young myocytes. Aged myocytes were less tolerant of high stimulus frequency (from 0.1 to 5 Hz) compared with young myocytes. Oxidative stress and protein oxidative damage were both elevated in the aging group associated with significantly enhanced p47phox but not gp91phox expression. In addition, level of cardiac AGEs was ∼2.5‐fold higher in aged hearts than young ones determined by AGEs‐ELISA. A group of proteins with a molecular range between 50 and 75 kDa with pI of 4–7 was distinctively modified in aged heart using one‐ or two‐dimension SDS gel electrophoresis analysis. These data demonstrate cardiac diastolic dysfunction and reduced stress tolerance in aged cardiac myocytes, which may be associated with enhanced cardiac oxidative damage, level of AGEs and protein modification by AGEs.