Catch one's breath and talk quietly (4)
I believe the answer is:
gasp
'catch one's breath' is the definition.
(I've seen this before)
'talk quietly' is the wordplay.
'talk' becomes 'gas' (I've seen this before).
'quietly' becomes 'p' (p for piano and quiet).
'gas'+'p'='GASP'
'and' acts as a link.
(Other definitions for gasp that I've seen before include "Breathe irregularly" , "Say "ah"" , "Breathe sharply in amazement, horror etc" , "Struggle for breath with open mouth" , "Puff, struggle for breath" .)