A heart murmur is an extra or unusual sound heard during a heartbeat. Murmurs range from very faint to very loud. Sometimes they sound like a whooshing or swishing noise.Normal heartbeats make a "lub-DUPP" or "lub-DUB" sound. This is the sound of the heart valves closing as blood moves through the heart. Doctors can hear these sounds and heart murmurs using a stethoscope. http://www.nhlbi.nih.gov/health/health-topics/topics/heartmurmur/
It is a sound we doctors can hear when the blood flow in the heart is more turbulent than usual. There are many types. The majority are"innocent flow murmurs" The rest are caused by valvular problems;either "leaky" valves or valves that are too tight( stenotic). Most often nothing has to be done but some need to be investigated.