When Crickets Cry by Charles Marten is an amazing book. I stayed up until 4:00 one weekend reading it.
Annie needs a heart transplant but her Aunt CeCe doesn't have the money to pay for it. Charlie lives life to the fullest in spite of his circumstances and his neighbor Reece isn't living at all except through his flashbacks. All these characters become woven together at a lemonade stand in a small town down South.
If I tell you any more it will ruin the twists and turns in the plot. There is some technical medical paragraphs to wade through but it's worth it!