Synonyms for Heart And Soul (same or very similar meaning)
WordNet sense 1 (the choicest or most essential or most vital part of some idea or experience):
center, core, essence, gist, heart, kernel, marrow, meat, nitty-gritty, nub, pith, substance, sum, inwardnessWordNet sense 2 (with complete faith):
body and soulFrom the ODE community, based on WordNetadd/edit