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 to rescue Peter Bishop, having a sudden cancer attack as the new universe renders him unable to heal. ("Over There: Part 2")
As Peter never existed to be rescued, James Heath would still be alive in the Alternate Timeline, though he remained unseen when David Robert Jones recruited the Cortexiphan subjects to create earthquakes, leaving his ultimate fate unknown. ("Worlds Apart")