Kang K et al. showed that using an in vivo rat MI model, a cell sheet of MSCs primed with Exo overexpressing CXCR4 (ExoCXCR4) was able to preserve heart function when applied soon after coronary artery ligation, whereas the MSC sheet exposed to control Exo was ineffective. Here, CXCR4 is linked to myocardial infarction.