You cannot say " I have no heart to do sth." For example, Chicken soup for soul, not for hearts. - G# K3 U% L5 Y/ k' KYour context is not very clear. So can you explain the contexts more clearly? * c. i% X+ j9 x- Q3 i% zWhy you don't want to bother the boy again?
For the first context, just say I am sorry to bother you again. 8 j& N. ^: W/ G1 qFor the second case, I don't think you can use hearts in this expression. You can say I am not meant to do sth...