"Related work" or "related works"

What is the context?

If the heading refers to things you produced in the same or relevant subject area, then work is uncountable, and the heading should be Related Work.

If the heading refers to your oeuvre or the output of a fellow artist, then work is countable in this case, and the heading should be Related Works.

Related Work

However, there are at least three cases where a distinction may need to be made.

1. If it is a list of literary items (works), then it could be plural: Related Works.
2. If it is a paragraph on other related work done by the author, then singular: Related Work.
3. If it is a list of engineering projects, then plural: Related Works.

In general it is singular: Related Work.

See also, some random examples from Wikipedia:
Australopithecus afarensis

If would depend on the context of the writing in question. If you want to pluralize work to works it should be in the case of referring to the body of work as multiple discrete items (ie works of art).

In the case of writing --

works

John had done a great deal of writing for clients in the past on these same topics. His related works included a blog post on Engadget and a magazine article for Wired.

work

John had done a great deal of related work writing on these same topics in the past.

This gets back to @Gnawme's point about the work being either countable or uncountable. If you can substitute stuff or another amorphous noun, then use work.

According to Google Ngram Viewer, the capitalized forms (as would be typical for section headings) are both used, but Related Work is considerably more common.