Actress Hayden Panettiere has passed away at the age of 36, confirmed by her representative to ABC News on Sunday. The cause of death is currently undetermined, though she was found in cardiac arrest. Panettiere was best known for her roles in “Heroes” and the country music drama “Nashville.” News of her passing has prompted an outpouring of grief from fans and colleagues. Authorities have not yet released further details regarding the circumstances surrounding her death. An investigation is underway to ascertain the specific cause of the cardiac arrest and subsequent passing. Further updates will be provided as they become available.