Earnest, heartfelt (7)
I believe the answer is:
sincere
I believe this is a double definition.
'earnest' is the first definition.
(sincere means earnest or genuine)
'heartfelt' is the second definition.
(similar in meaning)
(Other definitions for sincere that I've seen before include "True" , "'Genuine, not deceitful (7)'" , "Open and genuine, not deceitful" , "Honest, frank" , "Unfeigned, genuine" .)