Previous studies have shown that acute exercise preconditions the myocardium from ischemic injury. The purpose of this study was to test whether acute exercise protects the hypertensive myocardium from ischemia-induced diastolic rigor, and to compare the response between normotensive and uncompensated hypertensive hearts. Hearts harvested from female Wistar-Kyoto (WKY; n = 24) and spontaneously hypertensive rats (SHR; n = 27) (age:10-12 weeks) were exposed to ischemia (Langendorff isovolumic preparation; 22 minutes of no flow ischemia and studied following prior conditions of: 1) no exercise (WKY-CON, n=8; SHR-CON, n=8); 2) ischemia initiated one hour post-acute exercise (WKY-1HR, n = 8; SHR-1HR, n = 11); and 3) ischemia initiated 24 hours post-acute exercise (WKY-24HR; n = 8; SHR-24HR, n = 8). Acute exercise consisted of one bout of treadmill running at 25 m/min for 60 minutes. Heart weight was similar between WKY and SHR despite elevated in vivo resting systolic blood pressure and rate pressure product in SHR (P<0.05). During normoxic perfusion, left ventricular (LV) Langendorff performance was similar between WKY and SHR over the post-exercise time course. However, during ischemia, LV diastolic rigor was less in WKY vs. SHR (P<0.05). Acute exercise augmented ischemia-induced LV dysfunction one hour post-exercise in SHR (P<0.05), with gradual recovery by 24 hours post-exercise. These data suggest that acute exercise promotes ischemic diastolic rigor in SHR, even prior to the development of cardiac hypertrophy.