Dogs like Angel here have, thoughout history, risked their lives to save their owners. You can read more about Angel's story in the article linked to below.
But dogs can save us in a different way: By soothing us and relaxing us and lowering our blood pressure. This is not a trivial effect because it takes place daily, and it is the accumulated stress and accumulated relaxation that has the impact on your health in the long run.
Learn more about that here: Reduce Stress, Get a Dog