Ranted about heartless lady with passion (8)
I believe the answer is:
ardently
'with passion' is the definition.
(I've seen this before)
'ranted about heartless lady' is the wordplay.
'about' indicates an anagram.
'heartless' suggests removing the centre.
'lady' with its middle taken out is 'ly'.
'ranted' anagrammed gives 'ardent'.
'ardent'+'ly'='ARDENTLY'
(Other definitions for ardently that I've seen before include "In a very passionate way" , "full of enthusiasm?" , "Passionately" , "with zeal" , "With passion" .)