In the very beginning of the movie, Elsa accidentally hits Anna in the head with her ice and they frantically take her to the trolls for healing. In that scene the troll says that a frozen head is better than a frozen heart because it's easier to heal. He doesn't mention what needs to be done for a frozen heart at all.
Then, of course later in the movie, Anna does get hit in the heart. Only at. The curse Anna was under when Elsa struck her in the heart.
Elsa's fear makes her hit Anna with ice, accidentally freezing her heart. With Anna slowly freezing to death, Kristoff takes her to the trolls for help. Grand Pabbie says that only "an act of true love" can thaw her heart.
Kristoff races back to the castle so Hans can give Anna true love's kiss. Instead of kissing Anna, he says that. Comparison of Elsa and Anna's freezing and unfreezing scenes from Disney's Frozen in HD.
Anna is freezing solid after Elsa accidentally hits her heart with her powers. Hans turns out to be a bad guy, but his attempt to kill Elsa is foiled by Anna who steps between Hans and Elsa in the last moment before freezing. Her frozen body stops his sword.
Elsa cries since Anna sacrificed her life for her. But, since Anna showed an act of true love for her sister, she thaws. Elsa realises.
How does Elsa unfreeze Anna? Anna deduces that destroying the dam will release the enchanted forest from its curse and right the wrongs of the past. So that's what she does, with the help of the earth giants. When the dam breaks and the water begins to flow down the fjord, Elsa is freed from her frozen statue and her powers are returned to her.
Grand Pabbie says that only an act of true love can thaw Anna's frozen heart. Kristoff rushes off to Arendelle with Anna and the others so that she can get a kiss from her true love Hans. Anna thawed Elsa's heart and Elsa thawed Anna without realizing it.
Elsa had to love and accept Anna's love and since it's her magic she would have to unthaw Anna. Her magic isn't going to just do it on its own. It takes Elsa to do something, even if she doesn't realize it.
Otherwise, it doesn't make sense. Anna is willing to sacrifice her life for her sister. And that sacrificial act, truly brings life - 'Only a true act of love can thaw a frozen heart'.
Not only does this physically thaw Anna's heart, but also thaws Elsa's frozen heart. That act of true love helps Elsa to find a way out. Queen Anna of Arendelle (born June 21, 1825[3]) is the daughter of Agnarr and Iduna, younger sister of Elsa, and current queen of Arendelle.
She was extremely close with Elsa, but an accident during their childhoods prompted their parents to separate them from each other and the outside world. During the long years that followed, Anna tried repeatedly to spend time with Elsa but to no avail. the only reason why it could seem that elsa unfroze anna is because anna started unfreezing while elsa cried.
but I explained why anna didn't unfreeze immediately. and besides these two points, characters themselves prove it was anna in their conversation.