Hi J.,
I myself have a daughter with a severe heart defect, called "Ebstein Anomoly". She is now 16 years, and was given less than 1 percent chance to live at birth.
She had been through several bouts of pneumonias, and had been intebated twice.....one from about 10 days old to around 3 months old, and again around 9-1/2 months for RSV (a very dangerous lung infection for someone as small as my daughter was which can be fatal).
My advise is to let your daughter be as active as she wants to be. If the doctor seems to be ok, either you believe him or you do not. I myself, in my personal experiences have sought out new doctors. If you are not happy with the decision of the current doctor, you can get a second opinion.
The well being of you and your child are the most important thing. Doctors tend to forget what they went into there field for. They are not just healers, but they need to allow themselves to be human, and see when the patients need re-assurance from them.
Children are very resilient, and can do things that doctors say they will never do. Not all heart murmurs are bad, and having it checked out to see the severity of it is a good way to settle your unease, and this constitutes a the right to have it checked out.
I also have another daughter and grandson that have heart murmurs. My daughter grew out of hers, as the doctor stated she probably would. And that is what the doctors has told my daughter about my grandson. They have all been very active, and like to eat the more nutritious foods, instead of the junk.
Don't shelter them......let them be kids . If they have problems, you seem to be the type to see it before it would get out of control, and get the help they need. It's not easy to treat them the same way you would a child that does not have any health problems. But, they are just a tough!!
Saying a prayer for you.
LeAn A--
Cincinnati, Ohio