Saw, for example, in heart of Belgium (6)
I believe the answer is:
saying
'saw' is the definition.
(I've seen this before)
'for example in heart of belgium' is the wordplay.
'for example' becomes 'say' (I've seen this before).
'heart of' means to look at the middle letters.
The centre of 'belgium' is 'g'.
'say'+'in'+'g'='SAYING'
(Other definitions for saying that I've seen before include "Expressing in words" , "Gnome" , "Articulating" , "Adage, maxim" , "Apophthegm" .)