heart and soul vs nitty-gritty

heart and soul and nitty-gritty both are nouns.

Word	Noun	Adjective	Verb	Adverb
heart and soul	Yes	No	No	Yes
nitty-gritty	Yes	No	No	No

As nouns, heart and soul and nitty-gritty are synonyms defined as:

heart and soul and nitty-gritty: the choicest or most essential or most vital part of some idea or experience

Other synonyms of heart and soul include center, centre, core, essence, gist, heart, inwardness, kernel, marrow, meat, nub, pith, substance, sum.

heart and soul (noun)	nitty-gritty (noun)
the choicest or most essential or most vital part of some idea or experience	the choicest or most essential or most vital part of some idea or experience

heart and soul (adverb)	nitty-gritty (adverb)
with complete faith