I have a foster girl with a heart murmur, so I've recently learned more on this topic. A puppy heart murmur will often go away, so for now you probably should just wait and see what happens. If the murmur remains when your pup is an adult, additional testing should be done to determine the cause and severity of the murmur (by a cardiologist). That will help determine the prognosis and treatment options for you dog.
My girl recently had her testing done, and although their are no guarantees, the cardiologist does not believe that it will have any impact on the quality or length of her life, and he does not recommend any treatment or medication at this time. She's getting adopted this weekend by a wonderful family who will continue to monitor her condition and give her the care that she needs. They are a little nervous, but I'm so glad they are willing to give her a chance. She's 3 1/2 and a very spunky girl -- she shows no signs at all of being sick.