The symptoms of myocarditis may be subtle, making the diagnosis difficult, or the child may have obvious symptoms of heart failure. Clinical experience has shown the severity of symptoms or illness usually depends on the age of the child.
Children over 2 years of age may have fewer symptoms than newborns and infants who are usually more severely affected. This is thought to be due to the immaturity of a baby's immune system.
A child may get an infection during pregnancy (Rubella, for example) when it travels from the mother to baby. They are often breathing fast and having trouble feeding. They can be very fussy and difficult to console or very tired and sleep more than normal.
Blood will not travel through the body as well, and infants may have cool, pale hands and feet. The kidneys may also not work properly and there will be less urine produced.
There may be fever or other evidence of infection. In older infants, the findings are similar but there may be an associated weight loss due to trouble feeding.
Older children may have fewer symptoms. They may complain of a flu-like illness with of fatigue, malaise and fever.
They may not be able to tolerate exercise or may complain of chest pain or palpitations (skipped or extra heartbeats). They may develop a cough. Some children who have congestive heart failure may also have swelling in the face, feet or the legs. There may be belly pain and nausea due to swelling of the liver.
Due to poor blood flow, the liver and kidneys may be injured. The signs and symptoms of myocarditis are subtle early in the illness; therefore, it is not unusual for myocarditis to go unrecognized.
Myocarditis is sometimes diagnosed in retrospect when the child has an abnormal heart rhythm or is critically ill. It can also be diagnosed retrospectively in adulthood with abnormal heart rhythm or an enlarged heart.