"All" is a pronoun. It's one of those indefinite pronouns like "nothing" or "everybody". It is easy to forget that there are other pronouns besides the personal pronouns.
And, yes, I feel that the "of" is understood, hence elliptical.
I should have added that "all" is the object of theadverbial prepositional phrase "with all" and that it modifies "love". "(of) my heart" is and adjectival prepositional phrase modifying all -- What kind of all?
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