BUMC Medline Plus/OVID Tutorial:

Mapping Display

This is the Mapping Display. MeSH terms that match the phrase heart diseases will be shown in order of relevancy. The most useful subject heading will be at the top of the list.
In this case there is only one MeSH term matching heart diseases.

Your term mapped to the following Subject Headings:

Click on a subject heading to view more general and more specific terms within the tree.

Term is a thesaurus term

Include All Subheadings Combine selections with:

Select	Subject Heading	Explode	Focus	Scope
	Heart Diseases
	heart diseases.mp. search as Keyword

Remember: You do NOT want to search for heart diseases.mp. just yet.
This performs a text word/key word (title and abstract word) search INSTEAD of a subject heading search.
This would be a bad choice, because you would only retrieve articles that use the exact phrase "heart diseases." This search would miss relevant citations. Use the first option, the "heart diseases" subject heading instead.

Let's learn more about the EXPLODE and FOCUS options.

Click on the term heart diseases to see the Tree Display. It will show us what will happen if we EXPLODE.