Reckless bears, totally without heart (5)
I believe the answer is:
hasty
'reckless' is the definition.
(thesaurus)
'bears totally without heart' is the wordplay.
'bears' becomes 'has' ('have' can be a synonym of 'bear').
'without heart' means to remove the middle letters.
'totally' with its centre taken out is 'ty'.
'has'+'ty'='HASTY'
(Other definitions for hasty that I've seen before include "Rushed; rash" , "Precipitate" , "Reckless; hurried" , "Rash; thoughtless" , "Rashly quick" .)