If you have a mild case of myocarditis or are in the early stages, you might have no symptoms or mild ones, such as chest pain or shortness of breath.

In serious cases, the signs and symptoms of myocarditis vary, depending on the cause of the disease. Common myocarditis signs and symptoms include:

• Chest pain
• Rapid or abnormal heart rhythms (arrhythmias)
• Shortness of breath, at rest or during physical activity
• Fluid retention with swelling of your legs, ankles and feet
• Fatigue
• Other signs and symptoms of a viral infection, such as a headache, body aches, joint pain, fever, a sore throat or diarrhea

Myocarditis in children

When children develop myocarditis, they might have signs and symptoms including:

• Fever
• Fainting
• Breathing difficulties
• Rapid breathing
• Rapid or abnormal heart rhythms (arrhythmias)

Often, the cause of myocarditis isn't identified. Potential causes are many, but the likelihood of developing myocarditis is rare. Potential causes include:

• Viruses. Many viruses are commonly associated with myocarditis, including the viruses that cause the common cold (adenovirus); hepatitis B and C; parvovirus, which causes a mild rash, usually in children (fifth disease); and herpes simplex virus.

Gastrointestinal infections (echoviruses), mononucleosis (Epstein-Barr virus) and German measles (rubella) also can cause myocarditis. It's also common in people with HIV, the virus that causes AIDS.

• Bacteria. Numerous bacteria can cause myocarditis, including staphylococcus, streptococcus, the bacterium that causes diphtheria and the tick-borne bacterium responsible for Lyme disease.
• Parasites. Among these are such parasites as Trypanosoma cruzi and toxoplasma, including some that are transmitted by insects and can cause a condition called Chagas disease. This disease is much more prevalent in Central and South America than in the United States, but it can occur in travelers and in immigrants from that part of the world.
• Fungi. Yeast infections, such as candida; molds, such as aspergillus; and other fungi, such as histoplasma, often found in bird droppings, can sometimes cause myocarditis, particularly in people with weakened immune systems.

Myocarditis also sometimes occurs if you're exposed to:

• Medications or illegal drugs that might cause an allergic or toxic reaction.These include drugs used to treat cancer; antibiotics, such as penicillin and sulfonamide drugs; some anti-seizure medications; and some illegal substances, such as cocaine.
• Chemicals or radiation. Exposure to certain chemicals, such as carbon monoxide, and radiation can sometimes cause myocarditis.
• Other diseases. These include disorders such as lupus, Wegener's granulomatosis, giant cell arteritis and Takayasu's arteritis.

Severe myocarditis can permanently damage your heart muscle, possibly causing:

• Heart failure. Untreated, myocarditis can damage your heart's muscle so that it can't pump blood effectively. In severe cases, myocarditis-related heart failure may require a ventricular assist device or a heart transplant.
• Heart attack or stroke. If your heart's muscle is injured and can't pump blood, the blood that pools in your heart can form clots. If a clot blocks one of your heart's arteries, you can have a heart attack. If a blood clot in your heart travels to an artery leading to your brain before becoming lodged, you can have a stroke.
• Rapid or abnormal heart rhythms (arrhythmias). Damage to your heart muscle can cause arrhythmias.
• Sudden cardiac death. Certain serious arrhythmias can cause your heart to stop beating (sudden cardiac arrest). It's fatal if not treated immediately.