From the myth of Achilles onward, the heel stands for a weak spot in otherwise strong armour. Dreaming of it is read as awareness of where you are vulnerable.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.