Middle notes, otherwise known as heart notes or medium notes, become noticeable after the top notes have faded. They are the substance of the fragrance, lasting up to several hours. The middle notes determine the type of perfume (ie floral, spicy, oriental, etc).

Listing of essential oils which are used as middle notes in perfumes and colognes.

amyris

basil
bay
benzoin
bergamot
bitter orange
black pepper
boronia

cajeput
caraway
cardamom
cassie
cedarwood (atlas)
cinnamon leaf
clary sage
clove bud
coriander
cypress

fennel
frankincense

galbanum
gardenia
geranium
german chamomile
ginger
guaiacwood

hyacinth
hyssop

jasmine
juniper

labdanum
lavandin
lavender
lemon
lemongrass
lime
linden blossom

mandarin
may chang
melissa
mimosa
myrrh
myrtle

neroli
nutmeg

oakmoss
olibanum
orange blossom

patchouli
petitgrain
pine

roman chamomile
rose maroc
rose otto
rosemary
rosewood

sandalwood
spikenard
sweet marjoram
sweet orange

tagetes
tea tree
thyme
tuberose

vetiver
violet

yarrow
ylang ylang

See also:

Listing of essential oils which are used as Top Notes in perfumes and colognes.
Listing of essential oils which are used as Base Notes in perfumes and colognes.