Example
Search: heart beat
Query Translation: ("heart"[MeSH Terms] OR "heart"[All Fields] OR heart[All Fields]) AND beat[All Fields]
Search; “heart beat”
Query Translation: "heart beat"[All Fields]

From: NLM Catalog

Cover of The NCBI Handbook
The NCBI Handbook [Internet]. 2nd edition.
Bethesda (MD): National Center for Biotechnology Information (US); 2013-.

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.