Sweethearts are small heart-shaped candies sold around Valentine's Day. Each heart is printed with a message such as "Be Mine", "Kiss Me", "Call Me", and "Miss You". Sweethearts are made by the New England Confectionery Company, or NECCO.
The package from NECCO calls them "Sweethearts", which is the other common way of referring to them, but below that it says "tiny conversation hearts" as well as "#1 valentine candy." A similar type of candy is sold in the UK under the name Love Hearts.