Worry about heartless queen's visit (8)
I believe the answer is:
frequent
'visit' is the definition.
(I've seen this before)
'worry about heartless queen's' is the wordplay.
'worry' becomes 'fret' (fretting is a kind of worrying**).
'about' indicates putting letters inside.
'heartless' suggests removing the centre.
'queen' with its middle taken out is 'quen'.
'fret' enclosing 'quen' is 'FREQUENT'.
(Other definitions for frequent that I've seen before include "with extreme regularity" , "Happening often" , "Visit often" , "Common" , "Go to regularly" .)