Exposure to systemic hypoxia induces cardiac adaptive responses similar to ischemic preconditioning. We therefore, tested the role of hypoxia-induced agents such as Vascular Endothelial Growth Factor (VEGF) and Erythropoietin (EPO) in mediating myocardial preconditioning in response to acute intermittent hypoxia. Forty eight adult male Wistar rats (280-320 g) were assigned into 4 groups (n = 12 for each). Normoxic group (Nx), exposed always to normoxia prior to an ischemia/reperfusion protocol, and three Acute Intermittent Hypoxia groups (AIH, AIH3 and AIH8), subjected to brief cycles, 5 min, of hypoxia/reoxygenation for one hour in a closed chamber. AIH3 and AIH8 were sacrificed after 3 and 8 hours from hypoxia exposure, respectively, whilst AIH was exposed, similarly to Nx, to an ischemia/reperfusion protocol 24 hours after hypoxia exposure. Rats were anaesthetised with pentobarbitone sodium (40 mg.Kg^-1, I.P.) and the hearts were isolated and perfused in a retrograde manner in Langendorff apparatus (Radnotti, Harvard apparatus, USA) and subjected to in vitro global ischemia for 30 minutes followed by reperfusion. The following parameters were measured at baseline, during, and at the end of 120-minute reperfusion: heart rate, left ventricular developed pressure (LVDP), rate pressure product (RPP), peak left ventricular pressure rise (ΔP/Δt_max.). At the end of reperfusion, hearts were collected for subsequent reverse transcriptase polymerase chain reaction (RT PCR) and immunhistochemical analysis for the expression of VEGF and EPO. All animals were humanely killed at the end of the experiment. Significance (P<0.05) tested with one tailed unpaired t-test against the null hypothesis. Hearts of AIH displayed a significant improvement in post-ischemic haemodynamic measures compared to Nx controls, indicated by higher LVDP (76% recovery vs. 39% in Nx), RPP (76% recovery vs. 38%) and ΔP/Δt_max. (66% recovery vs. 43%). AIH caused a significant increased expression of VEGF and EPO by cradiomyocytes. This increased expression was detected at 3 and 8 hrs beyond the hypoxia/reoxygenation cycles (AIH3, AIH8) denoting early induction of VEGF and EPO genes by acute intermittent hypoxia. This increased expression of VEGF and EPO genes was also detected 24 hours following hypoxic exposure (AIH). Exposure of rat hearts to acute intermittent systemic hypoxia confers cardio-protective effects. This was evident by improved cardiac performance following ischemia/reperfusion. The improved post-ischemic cardiac function was associated with rapid induction of VEGF and EPO by cardiac cells that lasted for 24 hours later. Therefore, theses cytokines appear to play a role in mediating early and delayed cardiac adaptive responses to acute intermittent hypoxia. Hypoxic training could thus provide a new approach to enhance endogenous cardio-protective mechanisms.