A heart murmur is an extra or unusual sound heard during your heartbeat. Murmurs range from very faint to very loud and sometimes sound like a whooshing or swishing noise. Normal heartbeat sounds--"lub-DUPP" or "lub-DUB"--are the sounds of valves closing as blood moves through the heart. (Go to the section on "How the Heart Works" for more information about how the normal heart works.)