Preheat oven to 200 degrees, with racks in upper and lower third of oven. Combine egg whites and sugar in a bowl set over a pot of simmering water; stir until sugar dissolves and mixture is warm, about 3 minutes. Add salt and cream of tartar.
Beat with a mixer on medium-high speed until stiff, glossy peaks form and meringue is mostly cooled, about 7 minutes.
Transfer meringue to a piping bag fitted with a 1/2-inch plain pastry tip (such as Ateco #805). Pipe the letters L, O, V, and E, 3 times each, onto a parchment-lined baking sheet; each letter should be about 4 inches tall and spaced 1 inch apart. Pipe 16 hearts, 1 inch tall and 1 inch apart, onto another parchment-lined baking sheet.
Bake meringues until crisp on the outside but still soft inside, about 1 hour for letters and 40 minutes for hearts. Transfer to a wire rack and let cool completely. Cookies can be stored in an airtight container at room temperature up to 1 day.