Annexin A5 is a Ca2+ dependent phospholipid binding protein well known for its high phosphatidylserine affinity. In vitro, translocation to sarcolemma and externalization of endogenous annexin A5 in cardiomyocyte has recently been demonstrated to exert a pro-apoptotic effect. To determine whether these in vitro findings occurred in vivo, we performed myocardial infarction (MI) and studied time course of apoptosis and annexin A5 localization (0.5 h to 8 h) in the border zone around the infarcted area. This zone that was defined as Evans blue unstained and TTC stained, represented 42.3±5.5% of the area at risk and showed apoptotic characteristics (significant increases in caspase 3 activity (2.3 fold at 0.5 h; p<0.05), TUNEL positive cardiomyocytes (15.8±0.8 % at 8 h) and DNA ladder). Compared to sham-operated rats, we found that in this area, annexin A5 was translocated to sarcolemma as early as 0.5 h after MI and that translocation increased with time. Moreover, the amount of annexin A5 was unchanged in the border zone and decreased in the infarcted area after 1 h (77.1±4.8%;p<0.01 vs perfused area) suggesting a release in the latter but not in the former. In conclusion, we demonstrated that annexin A5 translocation is an early and rapid event of the whole border zone, likely due to Ca²⁺ increase. Part of this translocation occurred in areas where apoptosis was later detected and suggests that in vivo as in vitro annexin A5 might be involved in the regulation of early apoptotic events during cardiac pathological situations.