Many databases have a set of index terms or controlled vocabulary to define conditions; myocardial infarction instead of heart attack is an example used in MEDLINE’s Medical Subject Headings (MeSH). These terms describe the content found in the bibliographic record. They are arranged in a hierarchical structure with very broad terms at the top working down to more specific headings or narrow terms toward the bottom of the hierarchical list. Searching using controlled vocabulary terms yield more relevant results.

Ovid’s Subject Headings are shown here.  Myocardial Infarction is listed as a narrow term for the broader Subject Heading Heart Diseases.  Narrower terms are listed below the Subject Heading.  Cardiogenic Shock is more specific then Myocardial Infarction.