I had a murmer as a baby/young child. I don't think they tend to worry about these things, but just monitor them a little extra closely under stressful conditions (pregnancy is stressful on the body!). I wouldn't worry, but just keep an eye on it. If you feel especially out of breath or like it is palpatating more than usual, call you MW. Once you get into your later pregnancy though, being short of breath is somewhat normal. I know I can barely breathe as it is!