James Heath was a Cortexiphan test subject.
He is responsible for the death of his sister Julie Heath, because he transferred his cancer onto her temporarily. He goes on a cancer-transfer spree and is apprehended by the FBI, who place him into a coma. ("Olivia. In the Lab. With the Revolver")
Later, he has learned how to control his ability and heal others. He is the first person to die after the group travels to the Alternate Universe, having a sudden cancer attack as the new universe renders him unable to heal. ("Over There: Part 2")