DefinitionPediatric myocarditis is inflammation and weakness of the heart muscle in an infant or young child.Causes, incidence, and risk factorsMyocarditis is an uncommon disorder. In children it is usually caused by viral infections that reach the heart, such as the influenza (flu) virus, Coxsackie virus, and adenovirus. However, it may also occur during or after other viral or bacterial infections such as polio, rubella, Lyme disease, and others.When you have an infection, your body's immune system produces special cells that release certain chemicals to fight off disease. If the infection affects your heart, the disease-fighting cells enter the heart. However, the chemicals they produce can damage the heart muscle, causing it to become thick and swollen. This leads to symptoms of heart