OBJECTIVE: Physical activity has been shown to improve cardiovascular function and to be beneficial to type 2 diabetic patients. However, the effects of aerobic exercise (AE) on myocardial ischemia/reperfusion (MI/R) are largely unclear. Therefore, the aims of the present study were to determine whether long-term AE can protect the heart against I/R injury, and if so, to investigate the underlying mechanism. METHODS: Adult male Sprague-Dawley rats were randomly subjected to 8 weeks of either sedentary or free-loading swimming exercise (3 h/day, 5 d/week). Then the animals were subjected to 30 min MI followed by 4 h R. Arterial blood pressure and left ventricular pressure (LVP) were monitored throughout the whole MI/R procedure. Plasma creatine kinase (CK) and lactate dehydrogenase (LDH) activities were measured spectrophotometrically. Myocardial infarction and myocardial apoptosis (TUNEL analysis) were determined in a blinded manner. RESULTS: MI/R caused significant cardiac dysfunction and myocardial apoptosis (strong TUNEL-positive staining). Compared with sedentary group, rats subjected to 8 weeks of AE showed protection against MI/R as evidenced by reduced myocardial infarction (26.8 +/- 1.5% vs. 35.3 +/- 2.4%, n = 8, P < 0.05), inhibited cardiomyocyte apoptosis (decreased apoptotic index (12.4 +/- 1.1% vs. 21.0 +/- 1.7%, n = 8, P < 0.01) and decreased myocardial caspase-3 activity), decreased plasma CK and LDH activities and improved recovery of cardiac systolic/diastolic function (including LVSP and +/-LVdP/dt) at the end of R. Moreover, exercise resulted in 1.7-fold, 2.5-fold and 2.5-fold increases in Akt expression, Akt phosphorylation and glycogen synthase kinase-3beta phosphorylation in I/R myocardium, respectively (n = 3, all P < 0.05). More importantly, treatment with wortmannin, a PI3 kinase inhibitor, 15 min before R not only significantly blocked Akt phosphorylation (P < 0.05) in exercise rats, but also abolished long-term AE-induced cardioprotection for the I/R heart as manifested by increased apoptosis and myocardial infarction, and reduced cardiac function. CONCLUSION: Long-term AE exerts cardioprotective effect against MI/R injury, including anti-cardiomyocyte apoptosis, which is at least partly via PI3 kinase-dependent and Akt-mediated mechanism.