Rebecca, when "murmur" is used it's valves, I think (CHECK ME because I
am NOT sure), BUT I don't know if not losing those fetal blood vessels or
having a fetal-type of vascular overlay creates any noises which might
sound similar.  In such a case the ferret would often be having the blood
inadequately aerated and there are other possible serious problems.
 
For those who are curious: neural crest mutations don't usually seem to
affect the heart but since the rate of cardiac crest malformations is
higher in them it can do so (and also the rate is impossible to know
because almost no one necropsies dead infant kits or failed fetal ferrets
so it could be more than thought -- not likely to be fewer).  Those sorts
of malformations include vessels which are in a fetal path that it is
just plain wrong for the fully formed heart and lungs, or not losing some
fetal heart blood vessels which need to be lost for the heart and lungs
to operate properly for survival out of the uterus.  Most of these
individuals die in-utero OR die as infants (which is possibly one reason
that among a number of breeders the tragedy of lost kits of neural crest
disorder ferrets amounts to so very many avoidable deaths (as in a recent
case in which the female has had at least 17 kits born (if memory serves)
in multiple litters but so far only a scant handful kits have survived
just part of early infancy and who knows so far if those will make it),
and is one reason that many consider it a terrible and cruel choice to
breed such ferrets, especially coupled with the damage neural crest
disorders can do to the intestines, jaw, hearing, life-expectancy, etc.).
Also, neural crest disorder ferret females often have enough hearing
loss that it impacts badly on their infant care; they just can't use the
valuable tricks which non-hearing human parents can use.
 
Blazes, pandas, and other neural crest malformation ferrets just plain
should not be bred.  It is unfair.  Neural Crest mutations cause changes
to a very early cell type which later develops into a large range of
widely located cells with an assortment of functions.  The expression
of these mutations is variable, which means that the mutation itself is
constant as it is passed through the generations but how strongly it
expresses itself varies, so while one individual may be okay or mostly
okay the child or grandchild may have major health problems to struggle
through throughout life and in ferrets they may have greatly shortened
lives.
 
I realize that people have bred such ferrets BEFORE there was so much
information, and that some have bred then without knowing these things
and those people simple didn't know.  The ones who breed knowing these
things and who breed despite high death rates do worry me, though,
because quite simply I can't figure out any reasonable reason for them
to have done so once they know and begin to read the warnings out there
including from geneticists that there are no safe variants known among
ferrets and there is no way to modify any of the the neural crest
disorders to be safe, and that ferrets with the markings should be
sterilized.  (BTW, because of mutations, but far more often because of
variable expression, it is possible to have a ferret who appears normal
but carries one or more of these mutations.  It is also possible to have
an individual who has several neural crest mutations simultaneously
because there are multiple loci (genetic locations) which can harbor
mutated alleles that cause them.)
[Posted in FML issue 4520]