There is no particular duration of a Heart Murmur. An innocent Heart Murmur that occurs due to exertion can go away as soon as you stop doing the activity and relax. If you have a Heart Murmur due to fever, the Heart Murmur goes away as soon as the condition is treated. If your child has consistent innocent murmurs, they will go away on their own as he grows. When Heart Murmurs are caused due to an underlying heart problem, the Heart Murmur duration depends on the type of heart problem you have. While some can worsen over time, others gradually get better.