Deuteronomy 6.5
Septuagint

kai 
agaphseiV kurion ton qeon sou 
ex olhV thV dianoiaV sou, 
kai ex olhV thV yuchV sou, 
kai ex olhV thV dunamewV sou
 

New Testament - Matthew 22.37

o de efh autw: 
agaphseiV kurion ton qeon sou
en olh th kardia sou 
kai en olh th yuch sou 
kai en olh th dianoia sou

Mark 12.33

kai to 
agapan auton ex olhV thV kardiaV 
kai ex olhV thV sunesewV 
kai ex olhV iscoV 

Luke 10.27

o de apokriqeiV eipen: 
agaphseiV kurion ton qeon sou 
ex olhV thV kardiaV sou 
kai en olh th yuch sou 
kai en olh th iscuV sou 
kai en olh th dianoia sou

Septuagint

And thou shalt love the Lord thy God with all thy mind, and with all thy soul, and with all thy strength
 

New Testament

Matthew 22.37:  And he said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind

Mark 12.33:  and to love him with all the heart, and with all the understanding, and with all the strength

Luke 10.27:  And he answering said, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy strength, and with all thy mind

Masoretic Text

and thou shalt love Jehovah thy God with all thy heart, and with all thy soul, and with all thy might

Comments:  The NT inserts “with all thy heart” and replaces the Greek word dunamewV for strength with iscuoV.  The quotation from Mark shows even greater divergence employing “understanding” instead of “mind.”

The quotations agree with the LXX (against the Hebrew) in including the “mind” or “understanding” and with the Hebrew (against the LXX) in speaking of the “heart.”

The analysis shifts but reaches a similar conclusion if we consider a textual variant.  Brenton’s Septuagint is based on Codex Vaticanus.  Codex Alexandrinus gives “heart” where Vaticanus has  “mind.”  This variation brings the Septuagint into agreement with the MT; but the NT, inserting  “with all thy mind,” still differs from both the Hebrew and the Old Testament Greek.