I had two sizes of heart-shaped cutters, so I used the bigger one for the beet-mayo sandwich and the smaller one for Nutella and jam-filled sandwiches.
Take one slice of bread and place the cutters over them to get 2 heart shaped bread slices. If you have bigger cutters, make one heart-shaped slice for each slice of bread. Mine were smaller, so I got two heart-shaped slices, one big and one small.