“Can a heart murmur be fatal?”

A heart murmur is an abnormal heart sound and can be due to multiple reasons, mainly a problem with a heart valve. To determine how serious it is, he needs to know the cause of the murmur. First step would be to obtain an echocardiogram (a heart ultrasound) to evaluate the heart valves.

I recommend that your friend get an echocardiogram. That will determine the cause of the heart murmur, severity, etc.