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Myocardial infarction (MI) is the most common cause of heart failure (HF). Global incidence of heart failure is rising and there is no cure. Therefore, the development of effective therapeutics for heart failure is of the utmost importance and will be enabled by a deeper understanding of the mechanisms that drive endogenous regeneration in the heart. Reactivation of developmental genes as a response to injury is an important emerging paradigm of cardiovascular regeneration. We hypothesised that reactivation of fetal gene expression in adult cardiac endothelial cells (EC) promotes neovascularisation and cardiac regeneration after (MI).We analysed EC-specific single cell/nuclei RNA-sequencing data from 11 independent studies (60 total datasets) of developing and adult mouse and human hearts in healthy and post-MI states. Spatial transcriptomics was used to visualise gene expression in human MI. In both species, Annexin A2(ANXA2) was enriched in cardiac EC in development, undetectable in healthy adult EC, and reactivated in adult EC post-MI. Spatial transcriptomics showed specific upregulation of ANXA2 in the infarct border, a known site of heightened neovascularisation. Increased ANXA2 protein expression in human cardiac EC in MI compared to control hearts was confirmed using immunofluorescence (%ANXA2+CD31+/total EC: 77.1±12.1 vs 56.9±9.2, n=7/group, P=0.002).The functional importance of ANXA2 in vascular development and cardiovascular regeneration was studied in CRISPR/Cas9 anxa2ab knockdown dual-fluorescent zebrafish (Tg(fli1:eGFP)y1tg / Tg(myl7:DsRed2-NLS)f2) for simultaneous visualisation of blood vessels and cardiomyocytes. Anxa2ab CRISPants showed defects in vascular development with fewer intersegmental vessels/fish at 3dpf (23.3±3.1 vs 27.8±1.4, P<0.0001) and reduced GFP+EC numbers/fish at 5dpf (86.8±13.1 vs 99.0±12.7, P=0.049). Furthermore, anxa2ab CRISPants showed reduced diastolic endocardial ventricular volume (µm3) (8.6e6±2.0e6 vs 1.2e7±3.4e6, P=0.0006) compared to controls (n=20-69). 3dpf anxa2ab CRISPants had impaired regeneration at 48 hours post-cardiac laser injury (GFP+EC/fish = 61.7±21.3 vs 89.0±20.1, P=0.0001; mCherry+CM/fish = 56.6±17.0 vs 83.3±14.1, P=0.0001) compared to controls (n=20-24/group).Mechanistically, assessment of panels of markers of fibrinolysis, angiogenesis, and cardiovascular regeneration showed disruption to all 3 pathways with anxa2ab knockdown. In uninjured anxa2ab CRISPants, genes associated with angiogenesis were particularly affected with downregulation of tie1 (Log2 fold change= -1.1±0.3 vs -2.3e-11±0.2, P=0.0013), and vegfab (Log2 fold change= -0.6±0.3 vs -2.4e-11±0.2, P=0.0121). At 48 hours post-injury, CRISPants showed downregulation of fibrinolysis regulators, s100a10a (Log2 fold change= -1.0±0.5 vs -8.0e-11±0.2, P=0.0002) and s100a10b (Log2 fold change= -0.5±0.2 vs 3.3e-11±0.08, P=0.0023). Angiogenesis pathways were also dysregulated post-injury with reduced vegfab (Log2 fold change= -0.5±0.2 vs -0.08±0.1, P=0.0147) and cxcl12b (Log2 fold change= -1.3±0.8 vs 0.0±0.0, P=0.0063). Specific downregulation of the regeneration associated genes; notch1a (Log2 fold change= -1.2±0.3 vs 0.06±0.2, P<0.0001) and notch3b (Log2 fold change= -0.5±0.2 vs 0.03±0.1, P=0.0005) was observed.In conclusion, ANXA2 is reactivated in the adult heart post-MI and may be an important target for therapeutic neovascularisation and cardiac regeneration.