When an innocent heart murmur is triggered by fever, anxiety or exertion, it can disappear after the condition that triggered it goes away. In healthy children with more constant innocent murmurs, the murmur often becomes softer as the child grows and can eventually disappear completely.
When a murmur is caused by a heart problem, how long it lasts depends on the type of disorder. For example, some forms of endocarditis begin suddenly and get worse rapidly over a few days, while others cause milder symptoms over weeks or months. Murmurs caused by valve problems or congenital heart problems usually last throughout life, and in some cases, they can worsen over time.