Heat is a WiX data collection tool . You can run it in the directory to create the necessary WiX source code.
EDIT: If you want to use heat before creating a VS project, add it to your preliminary project events, as shown in the screenshot below (here's how I have my project setup for dynamically generating a WiX source for our ever-changing help content):

Pay attention to the switch -var wix.HelpSourcethat I have. Heat-generated WiX source files will set the location of the source files to this variable instead of hard coding. Thus, the generated source will have components that look something like this:
<Component Id="Welcome.htm" Directory="Content" Guid="INSERT-GUID-HERE">
<File Id="Welcome.htm" KeyPath="yes" Source="!(wix.HelpSource)\Content\Welcome.htm" />
</Component>
And in my particular case, I define this variable on the Tool Options screen of my VSX VS project in a relative directory ..\..\Help\Output, as shown below:

. , GUID , , . , GUID , , , , , WiX, GUID.