How common is tetralogy of Fallot?

Tetralogy of Fallot is the most common congenital heart defect. The word "tetralogy" means a group of 4, and in tetralogy of Fallot, there are 4 heart defects that occur in combination:

  • Ventricular septal defect (a hole in the wall of the heart [septum]).
  • Pulmonary valve stenosis (a narrowed or completely blocked pulmonary valve, which restricts blood flow from the valve to the lungs).
  • Malposition of the aorta (the aorta lies directly above the ventricular septal defect, as opposed to a normal heart, in which the aorta stems from the left ventricle).
  • Right ventricular hypertrophy (when the pulmonary valve is narrowed or blocked, it restricts blood flow out of the ventricle, causing it to thicken).

What are the effects of tetralogy of Fallot?

In a case of tetralogy of Fallot, blood flow to the lungs and the body is affected. Normally, the left ventricle pumps blood to the body and the right ventricle pumps it to the lungs. In tetralogy of Fallot, blood may flow across the ventricular septal defect (hole), from the right ventricle to the left ventricle, where it is pumped to the rest of the body. The blood pumped to the body lacks all of the oxygen it needs for organs to function properly.

The narrowed or obstructed pulmonary valve also limits the blood flow to the lungs. With pulmonary valve narrowing or blockage, the blood pumped to the lungs is low in oxygen because it is shunted through the ventricular septal defect, from the right ventricle to the left ventricle.

Because the blood pumped to the body has less oxygen than it needs, one of the symptoms of tetralogy of Fallot is a bluish tint to the skin, called cyanosis. Periodically, infants with tetralogy of Fallot can develop "tet spells." During a tet spell, the infant develops rapid, deep breathing, increased irritability, and prolonged crying, which in turn causes more intense cyanosis. Tet spells require immediate attention to calm the baby and "break" the spell. Emergency medical attention is required if the tet spell persists.

Last reviewed by a Cleveland Clinic medical professional on 04/28/2011.


  • Boni L, García E, Galletti L, et al. Current strategies in tetralogy of Fallot repair: Pulmonary valve sparing and evolution of right ventricle/left ventricle pressure ratio. Eur J Cardiothorac Surg 2009;35:885-890.

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