The incidence of diastolic heart failure increases dramatically with age. We investigated the impact of long-term exercise training on age-related diastolic dysfunction. Old (25-month-old) male Fischer 344 rats were studied after 12 weeks of treadmill exercise training or sedentary cage life (N=7, in each group). We determined cardiac performance using a pressure-volume conductance catheter and magnetic resonance imaging. Collagen volume fraction (CVF) and myocardial collagen solubility by pepsin as an index of advanced glycation end products (AGEs) cross-linked collagen were measured. The maximal slope of systolic pressure increment (+dP/dt) and the slope of end-systolic pressure-volume relation were higher, and end diastolic volume (EDV), Delta EDV (the percentage of the EDV increment-to-baseline EDV) and the slope of end-diastolic pressure-volume relation were lower in training group. The maximal slope of diastolic pressure decrement (-dP/dt) and time constant of LV pressure decay (tau) had no difference. AGEs cross-linked collagen, not CVF was reduced by exercise training. Long-term exercise training appears to attenuate age-related deterioration in cardiac systolic function and myocardial stiffness and could be reduce in pathologic AGEs cross-linked collagen in myocardium.