If stenosis of the mitral valve has occurred, giving a murmur, it could be the result of an underlying cause by infection or birth defect, making the heart work much harder than it needs to. This can lead to eventual heart
failure. Of course heart disease
can also cause the heart to adapt, enlarge, and force the mitral valve out of shape, making a murmur. So while a murmur itself doesn't give the pain, you can obviously have heart problems and pain while a murmur exists.