Will multiple h3 tags hurt my SEO?
The Frequently Bought Together widget product names are set by default inside <h3> HTML tags.
Urban legend says that having multiple <h3> tags is bad for SEO, but that is not true.
Multiple <h3> tags are perfectly correct following the HTML5 specification and will not negatively affect SEO.
Summarizing his words, it is normal to have repeated headers if they structure your store correctly.