i think your breeder is wrong, but, that is just my opinion, i think heart problems are just as prevelant in blacks, in fact, the greys i have known, including my own total 10 up north none of them had heart trouble, and, out of the blacks i knew, 2 had heart trouble, one was on our SAR team and died at 3 from SAS out of Tug Boat
the other outlived what doctors said he would, he had SAS and lived to 8 years.
i think it strange that it be said just greys would have this, but, than i have heard a lot o strange stuff said anyway!