What this tells me, is that the heart murmur
must be very very slight. And, with a slight murmur
in both of the babies, it is very likely to be a genetic thing. If only one of the babies had a heart murmur, I would think there was an abnormality that should be looked into.
I, personally, if they were mine, I wouldn't even worry about it especially if they were playing and eating normally. There are people that are born with heart murmurs, too.