We examined the effects of sprint-training on left ventricular diastolic stiffness during normoxia and following ischemia/reperfusion. Thirty seven, male Sprague- Dawley rats, weighing 150-175 g at the initiation of the experiment were randomly assigned to a sedentary, control group (N = 20), or a high intensity, sprint-trained group (N = 17). Animals were trained 5 d.wk^-1on a motor driven treadmill for 6 wk. High intensity sprint training consisted of running five 1- min sprints at 75 m.min^-1, 15% grade, interspersed with 1- min active recovery runs at a speed of 20 m.min^-1, 15% grade. Langendorff derived isolated heart performance was measured prior to and following 20 minutes of no- flow ischemia followed by 30 minutes of reperfusion. Isolated myocytes were harvested from a subset of post-ischemic hearts. Sprint-training reduced Langendorff-derived LV chamber stiffness (P<0.05) and induced a rightward shift in the LV pressure-volume relationship during both normoxic perfusion and following ischemia-reperfusion. LV developed pressure following ischemia-reperfusion was also better preserved in hearts obtained from sprint-trained animals (P<0.05), a result that is in part related to a lower post- ischemic LV chamber stiffness in sprint-trained hearts. The putative impact of sprint-training on post-ischemic LV chamber stiffness was masked by glycolytic inhibition with IAA, suggesting that glycolysis was involved in the better postischemic recovery observed in sprint-trained hearts. There was a tendency for enhanced post-ischemic cardiomyocyte shortening in sprint-trained cardiomyocytes compared to control. The rate of myocyte relaxation, i.e.T₅₀ relaxation at a given Ca²⁺ transient was similar between groups, suggesting that additional mechanisms unrelated to Ca²⁺ were involved in sprint- induced protection from ischemia-reperfusion- induced LV diastolic dysfunction.