Not so many in turmoil after change of heart (5)
I believe the answer is:
fewer
'not so many' is the definition.
('few' can be the opposite of 'many' so perhaps 'fewer' is reasonable for 'not so many')
'turmoil after change of heart' is the wordplay.
'turmoil' becomes 'few' (I can't justify this - if you can you should give a lot more credence to this answer).
'after' says to put letters next to each other.
'change' becomes 'conversion' (conversion is a kind of change).
'of heart' says to take the centre (I've seen 'heart of' mean this).
The central letters of 'conversion' are 'er'.
'few'+'er'='FEWER'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for fewer that I've seen before include "smaller number of people" , "Not so many" , "Less in number" , "in smaller numbers" , "Reduced" .)