Healing the Dying
When an adventurer is dying, any healing restores him or her to at least 1 hit point. If someone has stabilized the character using the Heal skill but he or she receives no healing, he or she regains hit points after an extended rest.
Regain Hit Points: When an adventurer is dying and receives healing, he or she is considered to have 0 hit points, and then regains hit points from the healing effect. If the healing effect requires the adventurer to spend a healing surge but he or she has none left, the healing still helps a bit: The adventurer’s hit point total is restored to 1.
Become Conscious: As soon as an adventurer has a current hit point total higher than 0, he or she becomes conscious and is no longer dying. (The adventurer is still prone until he or she takes an action to stand up.)
Example: Fargrim is at -12 hit points, unconscious and dying. His companion, Valenae the cleric, uses healing word to help him. This assistance immediately raises Fargrim’s current hit points to 0 and allows him to spend a healing surge, boosted by 2d6 extra hit points from Valenae’s healing word. Valenae gets a 6 on the dice roll, so Fargrim regains a total of 21 hit points (15 from the healing surge plus 6 from healing word). He is restored to consciousness with a current hit point total of 21.
Published in Player's Handbook, page(s) 295, Rules Compendium, page(s) 261.