Don’t put your headline in all-caps or all capital letters.
The eyes are creatures of habit. And they will attempt to read your all-caps one letter at a time.
This occurs because when your letters are in all-caps, there are no ascenders and descenders that would allow your eyes the ability to better recognize words.
People are used to reading things in lower case.
So don’t ask them to read the most important part of your marketing piece in a format to which they are not familiar. This creates one more avoidable mistake that will ultimately hurt your responde rates because far less people will make it past the headline and into the story you want to tell them.