A heart murmur is a sound made by turbulent blood flow in the heart. It sounds like whooshing or swishing with each heartbeat. Some adults and many children have incidental heart murmurs that are benign (harmless) and are not caused by abnormalities in the heart. However, some heart murmurs can signal an underlying heart problem.

Heartbeat: Anatomy of the Heart
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Benign murmurs are caused by the normal flow of blood through the heart and large vessels near the heart. The murmur may come and go over time. Some things that can increase blood flow and cause a benign heart murmur to be heard include:

Abnormal heart murmurs can be due to: