The Humane and Existing Alternatives in Research and Testing Sciences Act of 2025 (HEARTS Act of 2025) aims to significantly reform research practices at the National Institutes of Health (NIH) by prioritizing and promoting nonanimal methods. It amends the Public Health Service Act to ensure that all NIH-supported research fully evaluates scientifically satisfactory nonanimal methods before any animal use is approved or performed. This includes requiring research proposals to be reviewed by experts in nonanimal methods and providing incentives for their use. A key provision of the bill is the establishment of the National Center for Alternatives to Animals in Research and Testing within the NIH. This new center will be responsible for developing, promoting, and funding alternatives to animal research and testing, as well as creating a plan to reduce the number of animals used in federally funded research. Its duties include providing funding for the development of advanced nonanimal methods like 3D organoids and in silico modeling, training scientists, and fostering collaborations among research institutions. Furthermore, the bill mandates new reporting requirements for all federally funded research entities that use animals. These entities must report the number of animals used, disaggregated by species, every two years and make this information publicly available. They are also required to develop and submit plans for reducing animal usage to the National Center, with the goal of tracking progress and ensuring greater transparency in animal research. The term "animal" for reporting purposes is broadly defined to include any live, nonhuman vertebrate animal or cephalopod used in research or testing.