Purpose <p>Ischemia-reperfusion injury (IRI) poses a major challenge in cardiovascular therapy due to inflammation and oxidative stress. Ischemic postconditioning (IPoC) offers cardioprotection against IRI, but its efficacy may be compromised by chronic methadone use. This study examined the impact of IPoC on inflammatory and oxidative biomarkers in methadone-treated rats subjected to myocardial IRI.</p> Methods <p>Twenty-four male Wistar rats were divided into four groups: IRI, methadone-treated IRI (IRI-M), IPoC-treated IRI (IRI-IPoC), and methadone-treated IPoC-IRI (IRI-M-IPoC). Inflammatory proteins (IL-1β, IL-6, TNF-α), oxidative markers (SOD, GPx, TAS), and MDA levels were measured using commercial kits. Gene expression of inflammatory and antioxidant (NRF2, SOD, and GPx) was measured using Real-time PCR assay.</p> Results <p>IPoC significantly reduced the expression of inflammatory genes (IL-1β, IL-6, TNF-α, NF-κB) and enhanced antioxidant responses (NRF2, SOD, GPx) in rats subjected to myocardial IRI. Methadone-treated rats (IRI-M) exhibited elevated inflammatory markers and suppressed antioxidant gene expression. The combination group (IRI-M-IPoC) showed partial restoration of antioxidant activity and moderate reduction in inflammation, but these effects were significantly weaker than those observed in the IPoC-only group.</p> Conclusion <p>IPoC effectively reduces myocardial IRI by modulating inflammation and oxidative stress. However, chronic methadone use impairs these protective effects, likely through redox imbalance and enhanced inflammatory signaling. These findings confirm the need for optimized therapeutic strategies, potentially including antioxidant support, for patients on opioid maintenance therapy. Further research is warranted to clarify the molecular interplay between opioids and conditioning interventions.</p> Graphical abstract <p></p>