Turn southwest with lively heart (6)
I believe the answer is:
swivel
'turn' is the definition.
(swiveling is a kind of turning)
'southwest with lively heart' is the wordplay.
'southwest' becomes 'SW' (synonyms).
'with' means one lot of letters go next to another.
'heart' means to look at the middle letters.
The middle of 'lively' is 'ivel'.
'sw'+'ivel'='SWIVEL'
(Other definitions for swivel that I've seen before include "Kind of chair with seat that turns horizontally" , "Swing on a pivot" , "Turn on the spot" , "Revolving coupling" , "something pivotal" .)