The Heart Box is a small painted red hope chest with the golden latch resembling a conventional heart symbol with a gold dagger embedded with green jewels on it piercing through the heart.
It belonged to the Evil Queen, who gives it to the Huntsman to put Snow White's heart in after he kills her. But the Hunstman cannot go through with this evil task so he instead spares her life and urges the kind princess to flee into the forest to escape the Queen's wrath and eventually reaching to a small cozy cottage owned by the Seven Dwarfs. The Huntsman then puts the heart of a pig inside the box instead to fool the Queen. When she finds out from the Magic Mirror that she is holding the wrong heart, she is furious at being tricked and storms into her secret laboratory among the dungeons inside her castle, and tosses the box to the floor.
Many of the boxes appear in the ABC fantasy series, and are kept in Regina Mills' crypt that she has in Storybrooke during and after the first curse. However, Regina has had a huge amount of them in the dark castle, which her mother has in a secret volt in the castle, of all the hearts of the victims' lives she has taken. Regina mentions to Jefferson that she is unaware how many heart boxes her mother has but here are hundreds.
After the death of her lover, Daniel Colter, Regina becomes known as the Evil Queen and vows to take Snow White's heart and crush it. Thinking her daughter keeps failing, Cora takes the princess' heart and places it in one of the boxes until Prince Henry returns it to her.
On the first few days of the first curse, Regina is revealed to have Sheriff Graham's heart inside one of her boxes so she can control his every move, which Kurt Flynn sees before fleeing and is eventually killed. Many years later, after Regina turns good, her evil persona is released from inside her and continues the quest to destroy the lives of Snow and Prince Charming by taking out the heart they share and place it into one of the boxes, while putting them under a sleeping curse until the couple are freed.
In the original Brothers Grimm fairytale, the box itself is used to store the pig lungs and pig liver instead of the pig heart, which is brought to the Evil Queen by the Huntsman. The Evil Queen, thinking that those were Snow White's organs, proceeds to cook said organs into a stew which she then eats in a cannibalistic fashion, delighted in knowing that Snow White had been killed.
In the film Descendants, Evie, daughter of the Evil Queen, carries a bag/box that resembles the Heart Box.
The camera is always angled so that the pig heart itself is not visible, likely due to its graphic nature.