Open country to warm the heart! (5)
I believe the answer is:
heath
'open country' is the definition.
(I've seen this before)
'warm the heart' is the wordplay.
'warm' becomes 'heat'.
'heart' means to look at the middle letters.
The centre of 'the' is 'h'.
'heat'+'h'='HEATH'
'to' is the link.
(Other definitions for heath that I've seen before include "Scrubland" , "Moorland shrub" , "Common land; ex-PM" , "Statesman" , "Sir Edward - , PM" .)