Trees may be better than doctors at preventing cardiac deaths but they are themselves dying. Urban tree canopies are shrinking and cities lack resources to stop it. A research partnership of health professionals and environmentalists is planting 8000 trees in Louisville, one of the fastest warming cities in the US. They seek to discover the mechanisms by which trees benefit the hearts of their human neighbors and spark enthusiasm for greater investment in urban forestry. We talk with members of the research team from the University of Louisville, the City of Louisville's urban forester, the Nature Conservancy, and Louisville Grows, a local group which plant some of the trees.