Giant Cell Myocarditis

National Organization for Rare Disorders, Inc.

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It is possible that the main title of the report Giant Cell Myocarditis is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.


  • GCM
  • idiopathic giant cell myocarditis

Disorder Subdivisions

  • None

General Discussion

Giant cell myocarditis is a rare cardiovascular disorder that occurs for unknown reasons (idiopathic). It is characterized by inflammation of the heart muscle (myocardium), a condition referred to as myocarditis. Inflammation is caused by widespread infiltration of giant cells associated with other inflammatory cells and heart muscle cell destruction. Giant cells are abnormal masses produced by the fusion of inflammatory cells called macrophages. Individuals with giant cell myocarditis may develop abnormal heartbeats, chest pain and, eventually, heart failure. Many individuals eventually require a heart transplant. The disorder most often occurs in young adults.


The onset of symptoms of giant cell myocarditis is often rapid. Initial symptoms may include swelling of the ankles, chest pain, heart palpitations, fatigue, and shortness of breath (dyspnea) especially upon exertion or lying flat. Affected individuals eventually develop irregular heartbeats (arrhythmias) such as abnormally fast (tachycardia) or slow (brachycardia) heartbeats. Arrhythmias may cause sudden episodes of lightheadedness or loss of consciousness.

The abovementioned symptoms of giant cell myocarditis occur due to congestive heart failure or heart block. These two heart abnormalities are progressive and eventually result in life-threatening complications. In individuals with giant cell myocarditis, the average time from symptom onset to life-threatening complications or heart transplant is five and a half months.

The normal heart has four chambers. The two upper chambers, known as atria, are separated from each other by a fibrous partition known as the atrial septum. The two lower chambers are known as ventricles and are separated from each other by the ventricular septum. Valves connect the atria (left and right) to their respective ventricles. The valves allow for blood to be pumped through the chambers. Blood travels from the right ventricle through the pulmonary artery to the lungs where it receives oxygen. The blood returns to the heart through pulmonary veins and enters the left ventricle. The left ventricle sends the now oxygen-filled blood into the main artery of the body (aorta). The aorta sends the blood throughout the body.

Congestive heart failure is a condition in which abnormal enlargement or widening (dilatation) of one or more of the chambers of the heart results in weakening of the heart's pumping action, causing a limited ability to circulate blood to the lungs and the rest of the body. This leads to fluid buildup in the heart, lungs and various body tissues. In some cases, all four chambers of the heart may be affected. Symptoms may include fatigue, shortness of breath (dyspnea) upon exertion, swelling of the legs and feet, and chest pain.

Heart block may be partial or complete. In the mild form of heart block (first degree), the two upper chambers of the heart (atria) beat normally, but the contractions of the two lower chambers (ventricles) slightly lag behind. In the more severe forms (second degree), not all of the atrial beats are conducted to the ventricles. In complete heart block (third degree), the atria and ventricles beat independently. Individuals with first or second degree heart block may not experience symptoms (asymptomatic). However, individuals with complete heart block may experience episodes of unconsciousness (syncope), breathlessness, and/or fatigue.


The exact cause of giant cell myocarditis is unknown. Approximately 20 percent of cases occur in individuals with autoimmune disorders suggesting that autoimmunity may play a role in the development of giant cell myocarditis. Autoimmune disorders are caused when the body's natural defenses against "foreign" or invading organisms begin to attack healthy tissue for unknown reasons.

Autoimmune disorders associated with giant cell myocarditis include inflammatory bowel disease such as Crohn's disease. Some cases of giant cell myocarditis have been associated with a tumor of the thymus (thymoma). The thymus is a relatively small organ behind the breastbone that is thought to play an important role in the immune system until puberty.

Affected Populations

Giant cell myocarditis affects males and females in equal numbers. It can affect individuals of any age although the majority of cases occur in young or middle-aged adults (median age 42 years). Approximately 300 cases have been reported in the medical literature.

Standard Therapies


A diagnosis of giant cell myocarditis is made by biopsy of heart tissue. A biopsy is a test in which small tissue sample is surgically removed and studied microscopically. Tests to exclude other cause of heart abnormalities may also be performed. These tests may include echocardiogram and cardiac catheterization.


Standard and supportive treatment options for cardiac failure and arrhythmias are recommended. These treatment options may include the insertion of a pacemaker or implantable heart defibrillator.

Affected individuals may require a heart transplant. Affected individuals are often evaluated for heart transplantation shortly after diagnosis. In 20-25% of cases, infiltration of giant cells has recurred after heart transplantation. Immunosuppresssion with drugs that include cyclosporine prolong survival free of transplantation. GCM can recur after therapy in both the native and allografted heart.

Investigational Therapies

Researchers are studying the use of immunosuppressive drugs combined with steroids to treat individuals with giant cell myocarditis. For more information contact:

Myocarditis Program at Mayo Clinic

200 First St. S.W.

Rochester, MN 55905

Phone: (507) 284-4441


Information on current clinical trials is posted on the Internet at All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222

TTY: (866) 411-1010


For information about clinical trials sponsored by private sources, contact:

Contact for additional information about giant cell myocarditis:

Leslie T. Cooper Jr., M.D.

Director, Gonda Vascular Center

Professor of Medicine

Mayo Clinic

200 First Street SW

Rochester, MN 55906



Cooper LT Jr. Giant Cell Myocarditis. In: NORD Guide to Rare Disorders. Philadelphia, PA: Lippincott Williams & Wilkins; 2003:52-3.


Cooper LT Jr. Myocarditis. New England Journal of Medicine 2009;360:1526-38.

Cooper LT. Giant Cell Myocarditis in Children. Progress in Pediatric Cardiology. 2007;24:47-49.

Cooper LT, Okura Y. Idiopathic giant cell myocarditis. Curr Treat Options Cardiovasc Med. 2001;3:463-7.

Daniels PR, Berry GJ, Tazelaar HD, Cooper LT. Giant cell myocarditis as a manifestation of drug hypersensitivity. Cardiovasc Pathol. 2000;9:287-91.

Cooper LT. Giant cell myocarditis. Herz. 2000;25:291-8.

Cooper LT, Berry GJ, Shabetai R. Idiopathic giant-cell myocarditis/natural history and treatment. N Engl J Med. 1997;336:1860-6.


Myocarditis. May 2, 2012. Accessed June 28, 2012.


Myocarditis Foundation

100 W Main St

Utica, MN 55979

Tel: (732)295-3700

Fax: (732)295-3701

Tel: (866)846-1600



For a Complete Report

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