Inflamed Heart Muscle (Myocarditis) Viral, Drugs, Toxic, Immune

What is myocarditis?

Myocarditis is the medical term for inflammation of the muscular layer of the heart known as the myocardium. While the most common cause of myocarditis is a viral infection, which is often acute in nature, other causes such as toxins and  immune mediated reactions (drug hypersenitivity, post viral, and autoimmune) should also be considered as possible causes. The myocardium is the middle layer of the heart surrounded by the inner endocardium and outer epicardium. It is responsible for the contractions of the heart which circulates blood throughout the body. Inflammation of the heart muscle can be severe enough to cause permanent damage to the heart muscle and even lead to heart failure.

The causative factor in myocarditis causes injury to the heart muscle which results in inflammation. In the active phase, the swelling associated with inflammation causes the heart muscle to become enlarged although the heart itself is normal. As the disease progresses and in the chronic setting, hypertrophy may occur. With advanced cases the heart muscle may become flabby and while inflammation can resolve, there may be fibrotic scarring of the myocardium.

Causes of Myocarditis


Infectious causes are common in myocarditis and a viral infection of the myocardium (viral myocarditis) is the most common of the infectious agents. However, myocarditis may also arise with bacterial, fungal, protozoal and parasitic infections.

Some of the causative viruses involved in myocarditis include :

  • Coxsackie B
  • Echoviruses
  • Influenza (flu)
  • Adenovirus (cold)
  • Cytomegalovirus (CMV)
  • Epstein Barr virus (EBV)
  • Rubella (measles)
  • HIV

Other pathogens include :

  • Bacteria
    • Corynebacterium diphtheriae
    • Neisseria meningococcus
    • Borrelia (Lyme disease)
    • Chlamydia psittaci
    • Rickettsiae typhi (typhus fever)
  • Fungi like Candida
  • Protozoa
    • Trypanosoma cruzi (Chagas disease)
    • Toxoplasmosis
  • Helminths like trichinosis


In these instances the body’s immune system targets the heart muscle and causes inflammation due to one or more trigger factors, which may include :

  • drug hypersensitivity to pencillin, sulfonamides, anti-hypertensive and anti-epileptic drugs
  • post viral or bacterial (rheumatic fever) infection
  • autoimmune diseases like SLE (systemic lupus erythematosus)
  • transplants


Chemicals may be toxic to the heart muscle and therefore cause inflammation. This may include certain medication and toxicity in this regard should not be confused with drug hypersensitivity. In toxic causes of myocarditis, the drug may cause direct injury of the heart muscle whereas in hypersensitivity, the drug triggers the immune system to ‘attack’ the heart muscle.

Some substances and medication that may cause this type of myocarditis include :

  • Chemotherapeutic agents
  • Lithium
  • Narcotics like cocaine
  • Alcohol
  • Certain types of poisons

Other Causes

  • Giant cell myocarditis
  • Sarcoidosis
  • Radiation
  • Idiopathic (unknown causes)
  • Wegener’s granulomatosis
  • Endomyocardial fibrosis
  • Loeffler endomyocarditis
  • Endocardial fibroelastosis

Signs and Symptoms of Myocarditis

The clinical presentation depends on the causative factor and any complications of myocarditis that may have arisen. Many patients with acute viral infections may not experience any symptoms (asymptomatic) but ECG abnormalities and tachycardia (rapid heart rate) may be detected upon clinical examination.

  • Chest pain, typically behind the sternum (breast bone pain)
  • Palpitations
  • Rapid and/or irregular heart rate
  • Fever (infectious and sometimes immune-mediated causes)
  • Shortness of breath
  • Fatigue
  • Leg swelling

Additional symptoms may be related to the underlying cause, particularly infectious conditions, like diarrhea (viral gastroenteritis), sore throat (strep throat), headache, muscle aches, joint pain, runny nose and sneezing (rhinitis), cough and swollen lymph nodes.

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