Heart murmurs are sounds made by blood flowing through the heart's chambers or valves. They can be classified as innocent (harmless) or abnormal. Innocent murmurs are common in children and usually resolve on their own. Abnormal murmurs may indicate underlying heart problems, such as valve issues or congenital heart defects. The sound of a murmur can vary, often described as a whooshing or swishing noise. It is important to have any abnormal murmurs evaluated by a healthcare professional to determine their cause and significance.