A murmur is the sound of blood flowing through the heart and the largeblood vessels that carry the blood through the body. Murmurs can be a sign of a congenital (from birth) heart defect or can provide clues to illnesses that start elsewhere in the body and make the heart work harder, such as anemia or fever. In children, murmurs are often harmless and are just the sound of a heart working normally. These harmless murmurs are often called innocent or functional murmurs. Murmurs are easily heard in children because they have thin chests and the heart is closer to the stethoscope. When children have fevers or are scared, their hearts beat faster and murmurs can become even louder than usual.