Many times a heart murmur is heart with a new born, but goes away. Also, there is an innocent heart murmur and are common in children and almost alweays harmless. An innocent murmur may go a way and then return and some adults still have them.
Innocent murmurs are common in children and are quite harmless. In any group of children, a large percentage is likely to have had one at some time. Innocent murmurs also may disappear and then reappear. Most innocent murmurs disappear when a child reaches adulthood, but some adults still have them.
Do you have a heart valve(s) that leak greater than just mild, sight, etc. Has a serious valve disorder been diagnosed or are are just concerned about a murmur heard when you were a child? That may be medically insignificant.
It might effect you, it depends on the cause, and how it's being managed.
I've known of women who had defibulators in their chest, and went on to give birth to healthy babies. The OBGYN takes extra precautions, and the pregnancy is treated as high risk, but the outcome is usually good.
Congrats on the little one!