You know you are doing the Heart of Scrum if you are learning by frequently delivering ‘stuff' as a team.
You know you are doing the Heart of Scrum if, as emphasized by Dr's Takeuchi and Nonaka in the 1986 “Roots of Scrum” HBR paper, there is (1) built-in instability in which the group embraces change and can "turn on a dime, for a dime", (2) self-organizing teams in which teams demonstrate autonomy, self-transcendence, and cross-fertilization, (3) overlapping and "all at once" development in which there are no sequential phases or Sprints (no "design/testing Sprint", etc), (4) multilearning, in which individuals are doing multilevel and multifunctional learning, (5) subtle control in which the emphasis is on “self-control,” “control through peer pressure,” and “control by love," (6) a focus on organizational transfer of learning in which a learning organization has the five disciplines of personal mastery, reflection on mental models, the ability to create shared vision and group learning, and systems thinking.
You know you are doing the heart of Scrum, if the team owns and improves their process and ways of working every Sprint.
You know you are doing The Heart of Scrum, if the Development Team feel ownership of the Daily Scrum.
You know you're doing the Heart of Scrum if everyone involved with the project is always confident that they know as much as they need to, about what's going on, what's done, and what's coming up.