T-Max,
My Riley was also diagnosed with a heart murmur when he was 9 weeks old. The vet told me that they would keep an eye on it and that it could be gone by his next visit. Well, his next visit was this past Tuesday and the vet said it was indeed all gone. He now has a healthy heart.
The only advice that I can offer is to do what Matt S. asked, find out what grade the heart murmur was. Discuss it in detail with the breeder as well as the veterinarian. If it's a slight murmur chances are pretty good that he will grow up and out of it. If it's a severe murmur, well I won't go there because I really don't know what the results will be.
Regardless of the grade of the murmur, you have to make a decision of taking this pup or not. If it feels right to you, go for it. Just fully understand what you could potentially be getting yourself into before you jump into it. I hope I helped out!! Good luck and keep us posted!!!