I vaguely remembered a show (or possibly TV movie) about two (maybe middle school age) friends who have a crush on the same girl. The one friend had a heart condition and needs a transplant, and the other friend is a daredevil type kid. The daredevil kid gets killed doing a stunt (hit by a car I think), and he ends up being a match for the other kids heart and he ends up getting it. After he recovers, he starts trying to get close to the girl they had the crush on, but every time he does his heart starts to give out.
They end up finding out that the daredevil's soul is still in the heart, and his “spirit” is jealous of them being together.