Heading tags for WordPress
As mentioned here, the heading tags are <h1> <h2> <h3> <h4> <h5>
H1 heading for Blog title
H2 heading for post title, comment title and the sidebars.
H3 heading for the comment, and can be used manually as heading inside a post / article.
H4 heading can be used manually for a sub-heading / sub-section under H3.
Furhter reading: wordpress codex
