Ideally, you would be applying the heading style to an entire paragraph, not just part. Then use a Style Separator to separate your heading, that you want in the TOC, frcom the run-on part that you want to be part of the same logical paragraph.

• Headings that do not show up in the Navigation Pane or in a Table of Contents (or in Cross-References / Hyperlinks)
• TOC Tips and Tricks by Suzanne Barnhill, MVP - A TOC Entry for Part of a Paragraph