The Arnica genus is well known in herbal medicine. It has long been used in a variety of ways, and continues in use to treat bruises and arthritic pain. It does have some effect, with side effects of skin irritation that occurs only after prolonged use. Heartleaf grows in AK, AZ, CA, CO, ID, MI(E), MT, ND, NM, NV, OR, SD, UT, WA, WY, AB, BC, MB, NT, ON, SK, and YT. In Michigan, this species only occurs on Isle Royal and the Keweenaw Peninsula. Jefferson Co CO, 6/16/13.