A heart murmur is an abnormal "whooshing" or "swishing" sound heard with a stethoscope when there is unsteady blood flow near the heart. This sound is different from the usual "lub-dub" heartbeat sound. Heart murmurs can be loud or soft. Most of the time, they are harmless, but heart murmurs can sometimes indicate a heart condition that needs treatment. People of any age can have a heart murmur and the condition may come and go throughout a person's lifetime.