The Elixir of the Wounded Heart is a potion that has the ability to cure any wounded heart, both physically and emotionally.
Before the Curse
Robin steals the elixir from Zelena. ("Heart of Gold")
Robin and Marian get married and start a tavern together, but the Sheriff is spiteful and threatens to close it down should Robin prove unable to pay his taxes. He points out that Marian would be left alone on the streets with no one but he to comfort her, despite the fact that she tells him to his face that she will never be with him. Rumplestiltskin approaches Robin and offers him much gold in exchange for him traveling to Oz and stealing an important potion from the Wicked Witch. Robin is successful, also taking a magic bow that never misses its target, but gives the potion away to Will Scarlet instead, who needs it to get over the loss of his sister, leading him to realize that a man who steals for himself is selfish, but a man who steals for others is a hero. He decides to become an outlaw, robbing from the rich to give to the poor, and Marian decides to join him in this new life, wanting to be with him no matter what; he decides to change his name from Robin of Loxley to Robin Hood, which is more fitting for his new hoodlum lifestyle. She points out that Rumple would kill him if he ever saw him again, for he broke their deal, but Robin reveals that he stole the six-leaved clover from Oz, which allows him to change his form. ("Heart of Gold")
After the Second Curse
"Marian" keeps the elixir from Rumplestiltskin. ("Heart of Gold")
Robin heads to New York with Marian and Roland, intending to move into Neal Cassidy's apartment which Regina has given them the keys to. However, a common thief steals Marian's purse, and Robin chases him on horseback, eventually catching up and berating him for having no honor. When he and his family arrive at their new apartment, Mr. Gold turns up too, shocked to see people in his son's home. He has a sudden heart attack before he can kick them out, and Robin has him taken to hospital, where the Dark One realizes that all of his misdeeds have caused his heart to become poisoned. He employs Robin to steal Zelena's elixir of wounded hearts from Walsh's furniture shop, and he does so, for leaving a man to die goes against his moral code. He is successful in liberating it and gives it to Rumple; however, it doesn't work, but Marian switched the vials, soon revealing after Robin has left that she's Zelena in disguise. She followed Emma and Hook through the time portal, killed Marian when she was left unintended, and used the six-leaved clover of Oz to assume her form, having been playing everyone ever sine in order to dig at Regina's happiness. She wants Rumple to find the Author for her so that she can get a happy ending, and in exchange she will give him the elixir. Gold convinces Robin to stay with Marian, and the thief becomes reminded of why he loved her to begin with, deciding that she can still be his happy ending. He remains unaware that she's Regina's wicked sister in disguise. ("Heart of Gold")