Place cold eggs in single layer in saucepan. Cover with at least 1 inch (2.5 cm) cold water over top of eggs. Cover saucepan and bring quickly to boil over high heat. Immediately remove pan from heat to stop boiling. Let eggs stand in water for 18 to 23 minutes.
Drain water and immediately run cold water over eggs until cool enough to handle. Peel shells and discard.
Meanwhile, cut out 6 pieces from an empty, clean milk carton that measures 4 x 1.5-inch (10 cm x 4 cm); fold in half lengthwise.
Place an egg in centre of a cutout with narrow end pointy down. Top with a chopstick pressed deep enough into the egg to make an indent. Firmly secure chopstick to both ends of carton with elastic bands. Repeat with remaining eggs.
Chill for at least one hour. Carefully remove elastic bands and chopstick. Cut egg in half, through centre, to expose heart shape.