What a dilemma for you, I really donot envey your decision making ahead of you, only you and you alone can make the call, and i am sure you will do what is best for Ivy and you.

My older cat Ash has a heart murmur, i am not sure of the grade, but it is considered low, and he is fine, he sleeps more and tends to sneeze a lot,and has a few unwell days, but we are not sure if that is due to the problem or not, in general he is a healthy old boy for his age,despite the usual age related problems.

Good luck and i hope all works out well for you.