Heart Defect (Congenital) in Cats

Patent Ductus Arteriosus in Cats

The aorta is the main artery that feeds oxygenated blood from the left side of the heart to the body. The pulmonary (lung) artery carries deoxygenated blood to be oxygenated, traveling from the right side of the heart to the lungs. Once the blood has been oxygenated by the lungs, it then returns to the left side of the heart, through the pulmonary veins to be pumped out into the body by the aorta.

In the womb, the fetus’ descending aorta is connected to the pulmonary artery by the ductus arteriosus blood vessel, allowing blood to flow directly from the right side of the heart to the aorta, without stopping for oxygen in the lungs. This is because the fetus gets its oxygen from the mother's bloodstream and does not yet need to have its own blood oxygenated.

Normally at birth, this connection is no longer patent (open). Once a newborn has begun to breath on its own, the pulmonary artery opens to allow blood to flow from the right side heart into the lungs to be oxygenated, and the ductus arteriosus closes. But in patent ductus arteriosis (PDA) the connection remains patent. Consequently, blood is shunted (diverted) in abnormal patterns in the heart. PDA allows blood to flow from the aorta into the pulmonary artery, and then to the lungs.

If the shunt is moderate to large, it can cause left-sided congestive heart failure from blood volume overload on the left side of the heart. Less frequently, a large-diameter PDA will cause injury to the blood vessels in the lungs, from the excess amount of blood flowing into the lungs. High blood pressure in the lungs, and reversal of the shunt so that the blood goes from right to left (pulmonary artery to the aorta), as well as the typical PDA shunt direction of left to right (aorta to pulmonary artery) can be expected.

This atypical right to left shunting of a PDA can cause the aorta to carry blood that is low in oxygen, sending a signal to the body to produce more red blood cells (since they carry oxygen), making the blood too thick.

The condition or disease described in this medical article can affect both dogs and cats. If you would like to learn more about how this disease affects dogs please visit this page in the PetMD health library.

Symptoms and Types

  • Respiratory (breathing) distress:
    • Coughing
    • Exercise intolerance
    • Increased breathing rate
  • Right to left shunting PDA:
    • Hind legs are weak during exercise
    • Blood is thicker than normal, causing:
    • Arrhythmias (irregular heart beat)
    • Right to left blood clot
    • Pink, or bluish gums, and bluish skin around the anus or vulva
  • Possibly left-sided congestive heart failure
  • Rapid, irregular heart beat
  • Stunted growth


  • Genetic predisposition (i.e., birth defect)


Your veterinarian will perform a thorough physical exam on your cat, including a chemical blood profile, a complete blood count, a urinalysis and an electrolyte panel. You will need to give a thorough history of your pet's health leading up to the onset of symptoms. The level of oxygen in your pet's blood may also be tested, with samples taken from different locations for comparison.

Visualization of the heart, using radiograph and ultrasound imaging, is very instrumental for an accurate diagnosis of PDA. Often what will be seen in an X-ray is left heart enlargement; right to left (“reversed”) PDA will show a heart of normal size on an X-ray.

  Next >