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  • Synonyms
  • Signs & Symptoms
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  • Affected Populations
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  • Standard Therapies
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Hypoplastic Left Heart Syndrome


Last updated: September 17, 2007
Years published: 1986, 1993, 1994, 1996, 2003, 2007

Disease Overview

Hypoplastic left heart syndrome is a term used to describe a group of closely related rare heart defects that are present at birth (congenital). 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.

Hypoplastic left heart syndrome is characterized by the underdevelopment (hypoplasia) of the chambers on the left side of the heart (i.e., left atrium and ventricle). In addition, the mitral valve, which connects these chambers to each other, is usually abnormally narrow (stenosis) or closed (atresia) and the aortic valve, which connects the heart to the major vessels that lead from the lungs (ascending aorta), may also be narrow or closed. Infants with hypoplastic left heart syndrome also have an abnormally narrow ascending aorta.

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  • Aortic and Mitral Atresia with Hypoplasic Left Heart Syndrome
  • HLHS
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Signs & Symptoms

The symptoms of hypoplastic left heart syndrome are directly related to the underdevelopment of the left side of the heart and associated structures. In all cases, infants have impaired blood flow from the lungs, through the heart, and on to other parts of the body (systemic circulation). Symptoms may include difficulty breathing (dyspnea), a high-pitched noise while inhaling (rales), and grayish-blue discoloration of the skin (cyanosis) during the first 48 hours of life, which occurs because of low levels of circulating oxygen in the blood. Impaired blood flow characteristic of hypoplastic left heart syndrome results in fluid buildup in the heart, lung and various body tissues (congestive heart failure).

Infants with hypoplastic left heart syndrome may accumulate excessive acids in their blood and other body tissues (metabolic acidosis). Symptoms may include poor feeding habits, frequent vomiting, lethargy, and/or shock. When shock occurs, the symptoms may include abnormally high pulse (tachycardia) and respiration rate, respiratory distress, abnormally enlarged liver (hepatomegaly), cool moist skin, abnormally low blood pressure, and/or paleness. In most cases, if left untreated, life-threatening complications usually occur.

The progression and severity of hypoplastic left heart syndrome depend upon a structure called the ductus arteriosus, which is present in all newborns. The ductus arteriosus is a passageway that allows blood to travel from the right ventricle to the aorta and then throughout the body, bypassing the left side of the heart and the lungs. However, the ductus arteriosus closes shortly after birth forcing blood to travel through the malformed left ventricle resulting in impaired blood flow throughout the body.

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The exact cause of most cases of hypoplastic left heart syndrome is not known. It occurs for no apparent reason (sporadically) in the majority of cases. Research suggests that the interaction of many genes and other environmental factors (multifactorial inheritance) may be responsible for hypoplastic left heart syndrome. In some cases, autosomal dominant and recessive inheritance has been suggested.

In most cases, the malformations associated with hypoplastic left heart syndrome occur as a result of a developmental failure during early fetal (embryonic) growth. The reason that this occurs is not fully understood. Conditions that limit blood flow from the right to left atrium during fetal development may result in underdevelopment of the left heart. Such conditions may include premature closure of the foramen ovale and fetal heart muscle disease (cardiomyopathy).

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Affected populations

Hypoplastic left heart syndrome is a rare disorder that affects males (67 percent) more often than females. The estimated prevalence of the disorder is 1 in 100,000 live births. Hypoplastic left heart syndrome accounts for 7-9 percent of all congenital heart defects. The symptoms of this disorder are present at birth (congenital).

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The diagnosis of hypoplastic left heart syndrome is made based upon a thorough clinical evaluation, identification of characteristic findings and a variety of specialized tests. Such tests used to confirm hypoplastic left heart syndrome in newborns include x-ray examination and a special ultrasound test to study the structure and function of the heart (echocardiography).

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Standard Therapies


Treatment of hypoplastic left heart syndrome is directed toward the maintenance of adequate oxygen levels in the blood. The intravenous administration of prostaglandin E-1 (PGE-1) may help to keep the ductus arteriosus open allowing blood flow to bypass the malformed left side of the heart.

Eventually, infants with hypoplastic left heart syndrome require surgical intervention. In most cases, affected infants undergo a process that involves three separate surgical procedures (i.e., Norwood, hemi-Fontan, and Fontan procedures). The goal of this three-stage process is to separate systemic and pulmonary circulation. In some cases, affected infants have been treated by heart (cardiac) transplantation. A neonatal cardiologist is best qualified to give parents an opinion as to the type of treatment which best suits their child.

Other medications to prevent and control congestive heart failure may also be administered including digoxin and various diuretics. Antibodies, such as amoxicillin, may be used to treat infection of the valves of the heart (endocarditis) that may occur after heart surgery. Genetic counseling may be of benefit for families with a child who has hypoplastic left heart syndrome. Other treatment is symptomatic and supportive.

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Clinical Trials and Studies

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

For information about clinical trials being conducted at the National Institutes of Health (NIH) Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222

TTY: (866) 411-1010

Email: prpl@cc.nih.gov

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


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Mulreany M, Donner RM. Hypoplastic Left Heart Syndrome. In: NORD Guide to Rare Disorders. Lippincott Williams & Wilkins. Philadelphia, PA. 2003:50-1.

Behrman RE, ed. Nelson Textbook of Pediatrics, 15th ed. Philadelphia, PA: W.B. Saunders Company; 1996: 1325-28.

Buyce ML., ed. Birth Defects Encyclopedia. Dover, MA: Blackwell Scientific Publications; For: The Center for Birth Defects Information Services Inc; 1990:166-69.

Braunwald E, ed. Heart Disease. A Textbook of Cardiovascular Medicine. 3rd ed. Philadelphia, PA: W. B. Saunders Company; 1988:938-9.


Norwood Jr. WI, et al. Fontan procedure for hypoplastic left heart syndrome. Ann Thorac Surg. 1992;54:1025-9; Discussion 1029-30.

Farrell Jr. PE, et al. Outcome and assessment after the modified Fontan procedure for hypoplastic left heart syndrome. Circulation. 1992;85:116-22.

Starnes VA, et al. Current approach to hypoplastic left heart syndrome. Palliation, transplantation, or both? J Thorac Cardiovasc Surg. 1992;104:189-94; Discussion 194-95.

Jobes DR, et al. Carbon dioxide prevents pulmonary overcirculation in hypoplastic left heart syndrome. Ann Thorac Surg. 1992;54:150-51.

Jackson GM, et al. Intrapartum course of fetuses with isolated hypoplastic left heart syndrome. Am J Obstet Gynecol. 1991;165:1068-72.

Blake DM, et al. Hypoplastic left heart syndrome: prenatal diagnosis, clinical profile, and management. Am J Obstet Gynecol. 1991;165:529-34.

Bove EL. Transplantation after first-stage reconstruction for hypoplastic left heart syndrome. Ann Thorac Surg. 1991;52:701-4; Discussion 704-07.

Norwood Jr. WI. Hypoplastic left heart syndrome. Ann Thorac Surg. 1991;52:688-95.

Bailey LL, et al. Hypoplastic left heart syndrome. Pediatr Clin North Am. 1990;37:137-50.

Brenner JI, et al. Cardiac malformations in relatives of infants with hypoplastic left-heart syndrome. Am J Dis Child. 1989;143:1492-94.


McKusick VA, ed. Online Mendelian Inheritance in Man (OMIM). Baltimore. MD: The Johns Hopkins University; Entry No:241550; Last Update:2/19/94.

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