Organ part not primarily observed in heart area (6)
I believe the answer is:
cornea
'organ part' is the definition.
'cornea' can be an answer for 'part' (cornea is a kind of part). I am not certain of the 'organ' bit.
'not primarily observed in heart area' is the wordplay.
'primarily' indicates taking the first letters.
'observed in' indicates putting letters inside.
'heart' becomes 'core' (synonyms).
'area' becomes 'a' (maths abbreviation).
The initial letter of 'not' is 'n'.
'n' placed within 'core' is 'corne'.
'corne'+'a'='CORNEA'
Can you help me to learn more?
(Other definitions for cornea that I've seen before include "Body part" , "Clear part of the eye" , "Front covering of eye" , "Transparent part of the eye" , "bit of a looker" .)