S1[ edit ] The first heart sound, or S1, forms the "lub" of "lub-dub" and is composed of components M1 mitral valve closure and T1 tricuspid valve closure. Normally M1 precedes T1 slightly. It is caused by the closure of the atrioventricular valves , i. When the ventricles begin to contract, so do the papillary muscles in each ventricle.
Poor appetite and failure to grow normally in infants Heavy sweating with minimal or no exertion Chest pain Fainting When to see a doctor Most heart murmurs aren't serious, but if you think you or your child has a heart murmur, make an appointment to see your family doctor. Your doctor can tell you if your heart murmur is innocent and doesn't require any further treatment or if an underlying heart problem needs to be further examined. A person with an innocent murmur has a normal heart. This type of heart murmur is common in newborns and children. An abnormal heart murmur is more serious. In children, abnormal murmurs are usually caused by congenital heart disease.