A murmur is NOT an irregular heart beat
A murmur is only a noise made by turbulence in the blood flow through the heart. If air was moving through it instead and made noise, we would call it "whistling."
A murmur can last a lifetime. Those that start life with one may lose their murmur, those that start without one may get one as they grow older. Those that have one may get a second or third one if other parts of the heart starts creating turbulence and makes noise too.
A murmur cannot be compared from one person to the next, what part of the heart is making the noise, and when it is doing it, is the critical issue. Some murmurs
start soft and then get loud, others start loud and then gets soft, still others may have a steady tonal quality. So if someone starts their statement with: "I have a murmur too, and... blah blah blah" just ignore them. Unless they're a cardiologist doing an echocardiogram
on you, they won't have a clue as to what your murmur means.
A murmur's degree of loudness does not correlate to degree of disease. That is, loud does not mean sicker, and conversely soft does not mean better off.
A murmur may be medically meaningless or may signal doom. See your doctor for YOUR prognosis and what YOUR murmur means.
BTW: Here's a good page for everyone who wants to know to listen and hear what a murmur sounds like, the different kinds of murmurs, and what heart sounds
are like in general:
And FYI, even Wiki''s got a good page on murmurs: