I used DK red wool and a size 4 hook. (UK terms)
For the smallest heart:
Ch 4, make all following stitches in the 4th ch from hook:
3dtr, 3tr, ch1, dtr, ch 1, 3tr, 3dtr, ch3, slip stitch. Leave a tail long enough to make a chain to hang the decoration.
Medium heart:
1st round as for smallest heart, except ch 2 and ss at end.
2nd round: ch3, in first dtr: [dc, htr], in next st 2htr, in next 4 stitches: dc. Ch 1, tr in dtr, dc in next 4, 2 htr in next st, 3htr in next, [htr, dc] in next, ch 3, ss in centre. Leave a tail long enough to make a chain to join to the small heart.
Large heart:
Make medium heart as above, then:
3rd round: ch 3, dc in top of ch3 from previous round. 2dc in next st, dc in next, 2dc in next, then dc until the bottom point of the heart, ch1, 6dcs in next 6 stitches, 2dc in next st, dc in next, 2dc in next, ch3 and ss in centre. Leave a tail long enough to make a chain to join to the medium heart.
Make a chain to join each heart. ss into point of heart above in chain.