Hello, I’m an ACE certified personal trainer and I was also born with a heart murmur. It’s important to remember the murmur is not a condition in itself but a symptom of something going on in the heart. My cardiologist has placed no restrictions on exercise for me at this time, but it is important to check back with him every now and then. I would recommend talking to the client’s primary care physician or if possible their cardiologist. If nothing else this will give you more peace of mind when you talk to them about what specific activities you have in mind for the client.