Blaise Pascal’s a person to take heart from (5)
I believe the answer is:
unman
'to take heart from' is the definition.
(unman can mean to deprive of courage)
'blaise pascal's a person' is the wordplay.
'blaise pascal's a' becomes 'un' ('a' in French - Blaise Pascal was French).
'person' becomes 'man' (man is a kind of person).
'un'+'man'='UNMAN'
(Other definitions for unman that I've seen before include "Deprive of male qualities" , "Unnerve; make effeminate" , "Cause to lose courage" , "Take strength from" , "Take courage" .)