From Bulbapedia, the community-driven Pokémon encyclopedia.
The Sweet Heart (Japanese: ハート スイーツ Heart Sweets) is an item introduced in Generation V. It is made of very sweet chocolate. If the bag is sorted by type, it is located between Berry Juice and Fresh Water.
In the games
A number of Sweet Hearts are obtained through use of the C-Gear's Feeling Check, proportional to the "compatibility" of the two players.
|| Sweet Hearts obtained
If the player makes a bad movie in Pokéstar Studios, and it's not the last one in a series, several fans will give Sweet Hearts. Sweet Hearts could also be obtained in the Dream World area Pokémon Café Forest. A woman in Mistralton City will give one Heart Scale in exchange for ten Sweet Hearts. In Black 2 and White 2, on Valentine's Day (February 14) and White Day (March 14), the woman will allow the exchange for only five Sweet Hearts.
In X and Y, a Maid in Camphrier Town will give one away every day.
They restore only 20 HP to a single Pokémon when used.
|| Very sweet chocolate. It restores the HP of one Pokémon by only 20 points.
|| A piece of cloyingly sweet chocolate. When consumed, it restores 20 HP to an injured Pokémon.
Sweet Hearts are based on heart-shaped chocolates which are a popular gift between lovers. Their name is a pun on the term of endearment "sweetheart".
This is the artwork of the Sweet Heart as seen in the Pokémon Dream World.
| Sweet Heart