I - Rules
(see JITD, p. 15, 23)
When a hero suffers one or more wounds from a poison attack, the player first removes the appropriate number of wound tokens from his hero sheet, as normal. The player then places a number of poison tokens on his hero sheet equal to the number of wounds suffered in the attack. If the hero later receives healing, these poison tokens are removed first, one token per wound that would otherwise be healed. Once all of the poison tokens have been removed, the hero's wounds can be healed normally.
Example: A hero suffers two wounds from a poison attack. The hero player removes two wound tokens from his hero sheet, as normal. Then, he places two poison tokens on his hero sheet. Later in the game, the hero drinks a healing potion and would ordinarily recover three wound tokens. Because he is poisoned, he is only able to remove the two poison tokens and then recover one wound token.
II - References
Heroes with the Poison ability: none.