Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link

Tetralogy of Fallot


Lee B. Beerman

, MD, Children's Hospital of Pittsburgh of the University of Pittsburgh School of Medicine

Reviewed/Revised Apr 2023
Topic Resources

In tetralogy of Fallot, four specific heart defects occur together.

  • This condition includes four heart defects that can lead to oxygen-poor blood going directly to the body.

  • Symptoms include mild to severe cyanosis (a bluish discoloration of the skin due to lack of oxygen in the blood), life-threatening attacks of intense cyanosis due to a rapid drop in oxygen in the blood, and a heart murmur (a sound created by turbulent blood flow through narrowed or leaking heart valves or through abnormal heart structures).

  • The diagnosis is suspected based on a characteristic murmur and on the presence of cyanosis and is confirmed based on the results of echocardiography.

  • Surgery is required to correct the defect.

The four heart defects are

Tetralogy of Fallot: Four Defects

Tetralogy of Fallot: Four Defects

In infants with tetralogy of Fallot, the narrowed passage from the right ventricle restricts blood flow to the lungs. The restricted blood flow causes the oxygen-poor blood in the right ventricle to pass through the septal defect to the left ventricle and into the aorta (right-to-left shunt Shunting of blood flow About one in 100 babies is born with a heart defect. Some are severe, but many are not. Defects may involve abnormal formation of the heart's walls or valves or of the blood vessels that enter... read more ). The more oxygen-poor blood (which is blue) that flows to the body, the bluer the body appears.

Infants with severe or complete blockage of blood flow from the right side of the heart may depend on having an open ductus arteriosus for survival. The ductus arteriosus is a blood vessel in the fetus that connects the two great arteries leaving the heart, the pulmonary artery and the aorta (see Normal Fetal Circulation Normal Fetal Circulation About one in 100 babies is born with a heart defect. Some are severe, but many are not. Defects may involve abnormal formation of the heart's walls or valves or of the blood vessels that enter... read more ). After birth, the ductus arteriosus is no longer needed and usually closes within the first days of life. However, if the ductus stays open after birth in infants with severe tetralogy, some blood from the aorta can flow back into the lungs through the open ductus and thus pick up oxygen.

Symptoms of Tetralogy of Fallot

The main symptom is

  • Cyanosis (a bluish discoloration of the skin), which can be mild or severe

Infants with tetralogy of Fallot usually have a heart murmur. A heart murmur is a sound created by turbulent blood through narrowed or leaking heart valves or through abnormal heart structures.

Some children have life-threatening attacks (hypercyanosis or "tet" spells) during which cyanosis suddenly worsens without obvious cause or in response to activity, such as crying or having a bowel movement. The child becomes very irritable and short of breath and may lose consciousness. The heart murmur often disappears during these spells.

Diagnosis of Tetralogy of Fallot

  • Echocardiography

Doctors suspect tetralogy of Fallot based on a characteristic harsh murmur that can be heard with a stethoscope. In addition, oxygen levels are usually lower than normal when checked with a skin sensor (pulse oximetry).

Treatment of Tetralogy of Fallot

  • Sometimes a medication, such as a prostaglandin, to keep the ductus arteriosus open in the first week of life

  • For hypercyanotic spells, positioning, calming, oxygen, and sometimes medications and/or fluids given by vein,

  • An oral beta-blocker medication may be used after a hypercyanotic spell resolves until surgery can be done

  • Surgery

In infants who depend on an open ductus arteriosus for survival, giving a prostaglandin by vein to maintain an open ductus arteriosus can be lifesaving. Keeping the ductus arteriosus open sends extra blood to the lungs and increases the level of oxygen in the infant's blood.

Hypercyanotic spells

When an infant has a hypercyanotic spell, the infant may breathe more easily when the knees are close to the chest (knee-chest position). Interestingly, older children with tetralogy of Fallot will naturally do the same thing by squatting down, which helps to push more blood to the lungs and makes them feel better. Calming the infant and giving oxygen also help. If these measures do not work, morphine, fluids given by vein (intravenously), and medications such as a beta-blocker (for example, propranolol), or phenylephrine may be given to improve blood flow to the lungs.

Any infant or child experiencing hypercyanotic spells should have heart surgery promptly. A doctor may give the infant propranolol to decrease the risk of future spells if surgery cannot be done immediately.


In infants with tetralogy of Fallot, the defects need repair with surgery. If oxygen levels are low or infants have hypercyanotic spells, surgery is done in early infancy. If children have few symptoms, surgery is sometimes delayed until later in infancy.

If infants have low birth weight or have complex defects, doctors may use less invasive procedures to keep blood flowing to the lungs until surgery can be done. For example, they may use a synthetic blood vessel (a shunt) to connect the aorta to a lung artery. This procedure routes blood to the lungs so that more blood can obtain oxygen before it goes to the rest of the body. Another option can be done during cardiac catheterization, in which a thin tube (catheter) with an expandable flexible tube (stent) at its tip is passed through a blood vessel in the leg into the heart. The stent is expanded in the heart to enlarge the outflow to the lungs, which helps increase levels of oxygen in the blood.

During surgery, the ventricular septal defect is closed, the narrowed passageway from the right ventricle and the narrowed pulmonary valve are widened, and the patent ductus arteriosus is closed.

Children need to take antibiotics before visits to the dentist and before certain surgeries (such as on the respiratory tract) before and usually after surgical repair. These antibiotics are used to prevent a serious heart infection called endocarditis Infective Endocarditis Infective endocarditis is an infection of the lining of the heart (endocardium) and usually also of the heart valves. Infective endocarditis occurs when bacteria enter the bloodstream and travel... read more Infective Endocarditis .

More Information

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

Drugs Mentioned In This Article

Generic Name Select Brand Names
ARYMO ER, Astramorph PF, Avinza, DepoDur, Duramorph PF, Infumorph, Kadian, MITIGO, MORPHABOND, MS Contin, MSIR, Opium Tincture, Oramorph SR, RMS, Roxanol, Roxanol-T
HEMANGEOL, Inderal, Inderal LA, Inderal XL, InnoPran XL
4-Way Nasal, Ah-Chew D, AK-Dilate, Anu-Med, Biorphen, Formulation R , Foster & Thrive Nasal Decongestion, Gilchew IR, Hemorrhoidal , Little Remedies for Noses, Lusonal, Mydfrin, Nasop, Nasop 12, Neofrin, Neo-Synephrine, Neo-Synephrine Cold + Allergy, Neo-Synephrine Extra Strength, Neo-Synephrine Mild, Ocu-Phrin, PediaCare Children's Decongestant, PediaCare Decongestant, PediaCare Infants' Decongestant, Sinex Nasal, Sudafed PE, Sudafed PE Children's Nasal Decongestant , Sudafed PE Congestion, Sudafed PE Sinus Congestion, Sudogest PE, Vazculep
quiz link

Test your knowledge

Take a Quiz!