It really depends on the age of the dog. Often times a mild heart murmur in puppies will go away. When they are older, depending on the severity of the murmur it may or may not impact their quality of life. Many dogs and people live full healthy lives with a mild murmur. The more severe it is, of course the more impact there will be.
Neither I, nor my vet tech sister have ever heard of pred for a heart murmur. You should talk to your vet to see how severe the murmur is and why they have your dog on pred. Pred is not a nice medication and could cause more severe health problems if it is not needed for your dog.
There is no way to make a murmur go away, it is a defect and if it is a severe murmur surgery is required to repair it.
Good luck and talk to your vet before you do anything,
Charleen