Son faces hazard with extra heart, showing off (7)
I believe the answer is:
swagger
'showing off' is the definition.
'son faces hazard with extra heart' is the wordplay.
'faces' says to take the initial letters (I've seen 'face' mean this).
'hazard' becomes 'wager'.
'with' is an insertion indicator.
'extra heart' becomes 'g' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The first letter of 'son' is 's'.
'wager' going around 'g' is 'wagger'.
's'+'wagger'='SWAGGER'
(Other definitions for swagger that I've seen before include "Move confidently" , "Proud, pompous gait" , "Walk proudly" , "Boast" , "Blustering arrogance" .)