My second daughter had what they thought was a heart murmur
at birth. She had all the tests and then we were referred to a pediatric cardiologist.
He took a quick look at the tests then put the stethoscope on her chest and listened. First sitting up and then laying down. Then he told me it wasn't a heart murmur. It went away when she laid down. A heart murmur wouldn't go away.
It had something to do with the blood rushing down from her head into the blood vessels in her chest when she was upright. It made some noise. He called it venous hum and said she would outgrow it. She did. She's fine and a mother of two children now.
Stay calm. Even if it is a valve problem they can give medicine until she's bigger.