BACKGROUND The diagnosis of regional myocardial infarction (MI) after cardiac arrest and ischemia-reperfusion injury (IRI) is a major clinical challenge. OBJECTIVE We evaluated in a rat cardiac transplantation model whether IRI alone or with MI would induce complement C4d deposition. METHODS Isogenic heterotopic cardiac transplantation was performed in 16 Fischer 344 rats to induce IRI, of which 9 rats also underwent ligation of the left anterior coronary artery (LAD) of the heart to yield MI. Histology and qRT-PCR for endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS) and transforming growth factor β (TGFβ) were performed after cessation of heart beat. C4d was evaluated by immunohistochemistry. RESULTS Myocardial inflammation and C4d deposition was increased in grafts with IRI+MI as compared with IRI (0.71 vs. 0.14, PSU, respectively, p<0.04 and 80.13 vs. 20.29, PSU, respectively, p<0.02). The expression of eNOS decreased in grafts with IRI+MI as compared with IRI (p<0.05). Receiver operating characteristic (ROC) curve analysis showed that IRI+MI was associated with C4d deposition (AUC 0.837; S.E. 0.116; p=0.035; 95% C.I. 0.610-1.000). CONCLUSIONS Increased C4d deposition may be amenable to identify early MI after cardiac arrest. Early treatment aimed towards complement activation may provide a novel means for induced MI after cardiac arrest.