Heart attack, or myocardial infarction, is one of the leading causes of death worldwide. Although modern surgical techniques, diagnostics, and medications have greatly improved early survival from these events, many patients struggle with the long-term effects of permanently damaged tissue, and the 5-year mortality rate remains high. Now, researchers from Suzhou Dushu Lake Hospital, Suzhou , China, and North Carolina State University and University of North Carolina-Chapel Hill, reporting online on June 21, 2021 in ACS Nano describe developing a minimally invasive exosome spray that helped repair rat hearts after myocardial infarction. Scientists have explored using stem cell therapy as a way to regrow tissue after a heart attack. But introducing stem cells directly to the heart can be risky because they could trigger an immune response or grow uncontrollably, resulting in a tumor. Therefore, researchers have tried injecting exosomes –– sub-cellular, membrane-bound sacs containing proteins, lipids and nucleic acids secreted by stem cells (and by all other cells examined)--into the heart, but the exosomes often break down before they can have therapeutic effects. Others have developed cardiac patches, or scaffolds that help implanted exosomes last longer, but they usually must be placed on the heart during open-chest surgery. Dr. Yafeng Zhou (Suzhou Dushu Lake Hospital) and colleagues wanted to develop an exosome solution that could be sprayed onto the heart through a tiny incision, avoiding major surgery.