So, hard hearted, you quickly gain a high position (4)
I believe the answer is:
soar
'you quickly gain a high position' is the definition.
I can't judge whether this definition defines the answer.
'so hard hearted' is the wordplay.
'hearted' says to take the centre.
The central letters of 'hard' are 'ar'.
'so'+'ar'='SOAR'
Can you help me to learn more?
(Other definitions for soar that I've seen before include "'Fly, glide (4)'" , "take to the air" , "Rise to a great height" , "Move quickly upward" , "Rise effortlessly" .)