Is a heart murmur dangerous

There are more than one reason, sometimes when a woman is pregnant, or if someone is anemic, the heart will have a "conpensatory systolic heart murmur" to just add an extra beat of the heart to give the body a little extra oxygenated blood every few beats. Also sometimes when their is a mitral valve problem, the heart will have a murmur.Often after the anemiais taken care of or the baby is born the murmur will just disappear.