How serious is a left to right shunt and what will it take to repair it?

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Submitted by Dr T on September 20, 2010 – 10:06am

Circulation in a nutshell:

Normally, O2 poor (“Venous”) blood from the right side of your heart goes to the lungs where CO2 is removed and replaced with O2. This is called the ‘Pulmonary” circulation. It then returns to the left side of your heart where the now O2 rich (“Arterial”) blood is pumped to the rest of your body to supply it with Oxygen. This is called the “Systemic” circulation. When that is done, your blood is now again O2 poor and thus venous, and returns to your heart to start this cycle anew.

In other words, blood first makes its way through the systemic circulation, then the pulmonary circulation, then back to the systemic circulation, and so on.

A left-to-right shunt is when blood from the left side of the heart goes to the right side of the heart, without first going through the systemic circulation. This can occur either through an opening between the division (“Septum”) that divides the left and the right side of your heart or trough a persistent “duct” of the artery (the Aorta) leaving the heart. In Left-to-right shunts the blood pressure in the left side of your heart is higher than the right side (as it should be), and thus will flow to the lower pressure right side of the heart if there is an opening.

Besides medications, treatment may include surgery to close the opening or close the duct. Sometimes emergency surgery is needed even in premature infants.

This is what a normal circulation looks like before birth (click on the image):

This is what it looks like after you are born and your Umbilical cord is cut (click on the image):

Left to Right Shunts

You can think of Left to right shunts as a “back-leak” of blood from the systemic to the pulmonary circulation. As a consequence, the pulmonary circulation carries not only the blood from the right side of your heart, but also the additional blood entering via the left side of your heart or from the systemic circulation. Blood volume and pressure in the pulmonary circulation become thus abnormally high. If this shunt is significant, there is progressive damage to the pulmonary vasculature and gradual development of irreversible changes in your heart and lungs.

Because of the extra flow that goes to the “right heart” and the pulmonary circulation, which are not built to handle that much extra blood, one can hear abnormal heart sounds (“murmurs”), and if not treated this part of the heart may start to fail.

Lesions resulting in left to right shunts include :

  • Ventricular septal defect (VSD)
  • Patent ductus arteriosus (PDA)
  • Atrial septal defect (ASD)
  • Atrioventricular defect (AVSD)

You can see here what some these look like (the “blue” side is the right side of your heart):

Persisting ductus arteriosus (PDA)

The PDA is located where you see no. 1

Atrial septum defect (ASD)

Ventricle septum defect (VSD)

Symptoms and Signs include

  • Murmurs
  • Heart Failure signs may include

Rapid heartbeats and breathing
Shortness of breath with feeding

Diagnosis probably will include these type of tests:

  • Testing the Oxygen content in the blood, ECG, and chest x-ray
  • Cardiac ECHO
  • Cardiac Catherization


  • Medical treatment of Heart Failure
  • Surgical repair with open heart surgery

Hope this was helpful,

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