Several recent studies have found that pregnant women who use Zofran are more likely to have a baby with a ventricular septal defect, which is a life-threatening “hole in the heart” defect.

Zofran and Ventricular Septal Defect

Zofran (ondansetron) is often used during the first trimester to prevent morning sickness caused by pregnancy. The first trimester is also when most major heart defects occur.

Unfortunately, a growing number of studies suggest that Zofran may increase the risk of birth defects. In December 2014, Reproductive Toxicology published a study linking Zofran with a 62% increased risk of heart defects.

The study also linked the use of Zofran in early pregnancy with a doubled risk of cardiac septal defects, including atrial septal defect and ventricular septal defect.

In 2013, another study involving 900,000 pregnancies in Denmark from 1997-2010 found a 30% increased risk of major birth defects associated with Zofran, mostly due to a doubled risk of heart defects.

What is Ventricular Septal Defect?

Ventricular Septal Defect (VSD) is a “hole in the heart” defect that occurs when there are holes in the wall (“septum”) that normally separates the two lower chambers of the heart. The defect occurs during the first eight weeks of pregnancy.


Normally, the bottom-right chamber of the heart (right ventricle) is responsible for pumping oxygen-poor blood from the body into the lungs. Oxygen-rich blood from the lungs passes through the lower-left chamber (left ventricle) and is pumped into the body through the aorta.

When there is a hole between the left and right ventricles, oxygen-rich blood mixes with oxygen-poor blood. This results in mixed blood being pumped into the body. The heart must work harder to compensate, resulting in higher blood pressure in the lungs (pulmonary hypertension).

Over time, pulmonary hypertension permanently damages delicate blood vessels in the lungs. The muscle in the right ventricle can also thicken, lose flexibility, and weaken until it is no longer able to pump blood effectively. This can lead to deadly heart failure.


  • Heart murmur (abnormal sound heard with a stethoscope)
  • Fatigue
  • Sweating
  • Rapid and heavy breathing
  • Poor feeding or tiring easily while feeding
  • Failure to gain weight or thrive


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