When defining a view in the Heat map, you can choose between various fields, which will be shown as columns in the report. You should be able to include all fields from the object, but some fields may be hidden for you due to field-level security.
If you are not able to include a specific field, please check with your system administrator whether you have access to the field in question.
In case you are the system admin, we have outlined below how to change the field-level security - please observe that this is standard Salesforce functionality.
Here is an example: Say we want to make the field "Expected amount" available for a group of users in the heat map for opportunities.
First, choose the menu path: Set up -> Customize -> Opportunities -> Fields
Locate the relevant field in the list, and click on the field. Press Edit.
Set the Field-Level Security to Visible for the relevant user profiles. Press Save.