Lively end to working week: heaven (6)
I believe the answer is:
frisky
'lively' is the definition.
(I've seen this before)
'end to working week heaven' is the wordplay.
'end to working week' becomes 'fri' (abbreviation for Friday).
'heaven' becomes 'sky' (I've seen this in another clue).
'fri'+'sky'='FRISKY'
(Other definitions for frisky that I've seen before include "Frolicsome" , "Lively like playful dog" , "High-spirited" , "Animated" , "Playful, full of energy" .)