How did the Lernaean Hydra’s poison contribute to Heracles’ death?

Heracles dipped his arrows in the Hydra’s poisonous blood after killing the monster. He later used one of these arrows to kill Nessus, a centaur who had tried to assault Heracles’ wife, Deianeira. Nessus’s blood became contaminated with the poison. Deceived by Nessus, Deianeira put the blood on a garment for Heracles. The poison entered his body and ultimately caused his death.