Two ailing boys from two different worlds have what each needs to live. The price is just right for the exchange… except not everyone is keen on having them alive.

This logline is too vague. Is one of the boys MORE sympathetic, or experiences GREATER change than the other? Then he's your protagonist. Write the logline from his perspective.

I am assuming, from the title, that what they need is each others hearts? This doesn't make sense? You need to be clearer to entice interest.

Who is putting a price out? Who is the antagonist? You're not creating an air of mystery and intrigue, you're making me work too hard for the BASICS of the story. I want to know WHO your film is about, WHAT it is about (the goal and stakes) and WHO is trying to stop them. It's those elements that will tell me whether your film has a hook ... and will tell any potential investor whether it's worth making, and any potential audience whether it's worth watching.