Hi here again some video material I found and did want to share with you all. Those video's were made before the DNA test was available, but wil provide you with some more information about DM.
http://www.akcchf.org/video/viewer.cfm?vid=1
And when you have a dog with DM here is a video how to care for this dog, I don't think I would go that far with a dog of mine.. but that is something that every owner has to deside for himself.
http://www.akcchf.org/video/viewer.cfm?vid=2
So I think we have the tool now to get rid of this problem in the future, see for yourself and again... wise decisions to be made.