Removing h3s in excerpt output?

There’s a discussion on WP Support Forum that was related to your question. The pastebin constains the function stated in the other answer.

I’ve decreased the priority to 5 and it works on my test theme.

add_filter( 'get_the_excerpt', 'wp_strip_header_tags', 5);

If you want to target only <h3> you can use this regex:

$regex = '#(<h([3])[^>]*>)\s?(.*)?\s?(<\/h\2>)#';