My 8month old diagnosed heart murmur. He is healthy, growing well, developing. In pregnancy had heart sono, all was well. Chance of murmur being innocent?

Very good. Most of the "murmur bad" group are discovered by age 2 mo. through a variety of physical findings or testing. In decades as a pediatrician, I think I heard an innocent murmur at some point in most of my kids. It was became so common and the findings so predictable, I often just monitored them for years without any testing.These often disappeared with age.