Not only does this defect hinder breathing in the kitten, but it also makes it harder for the heart to pump blood. The blood tends to thicken and too much is circulated through the left side of the heart. This causes half of the heart to enlarge and leads to heart failure, which is a life-threatening condition. Fluid will also begin to build in the lungs. Identifying this defect early is crucial to allow treatment to be effective before irreparable damage has occurred. This issue is seen more often in female kittens, and up to 50 percent of cats born with this defect will die within their first year if it is left untreated.

Kittens developing in the womb have a blood vessel called the ductus arteriosus that is responsible for helping most of the blood bypass the lungs, as they are not used in utero. The blood vessel connects two of the main arteries; the aorta and the pulmonary artery. Shortly after birth, this blood vessel closes off, allowing the lungs to receive more blood flow to help the kitten breathe properly. Some cats are born with a defect that stops the ductus arteriosus from closing off, severely limiting the blood that reaches the lungs. This is referred to as “patent ductus arteriosus” (PDA).

Signs of this problem will worsen as time goes on. Severe symptoms will show as the heart and lungs become damaged. A list of potential warning signs is below.

In the past, it was thought that this condition rarely formed in cats, however more and more cases are reported as time goes by. One possible reason for this is that many kitten deaths are not assessed by a veterinarian, although in recent years, more people have their kittens properly monitored. PDA is now thought to be the most common “shunting” heart defect that occurs in cats. It is passed down genetically, and certain breeds, such as the Siamese, are more susceptible to the defect than others. 

This birth defect is most often discovered as part of a kitten’s first veterinary check-up. During the routine examination, a machinery (continuous) heart murmur may be heard while assessing the heartbeat with a stethoscope. This happens because the blood is flowing in a chaotic manner. An X-ray of the chest can reveal abnormal size or shape of the heart, in addition to showing if there is fluid present in the lungs.

An electrocardiogram measures the electrical activity of the heart and will make any arrhythmia (abnormal heart rate) known. Tachycardia, or a rate far higher than normal, is often seen in kittens with PDA. An echocardiogram (ultrasound of the heart) can reveal how the inside of the heart is functioning. It can also help the veterinarian to rule out any other possible defects or heart conditions that could be causing the symptoms. Diagnostic imaging will also show if the left side of the heart is larger than the right. Full blood work should be run, including a complete blood count and a biochemical profile. The CBC may show elevated red blood cell levels and packed cell volumes, indicating that the blood is overly thick.

To permanently fix the defect, the blood vessel will have to be closed. This needs to be done as soon as possible to prevent other harmful conditions from arising. The kitten may not respond to anesthesia well if the heart is already damaged. A special veterinary surgeon is required for all treatment procedures of this defect.

This surgery involves making an incision directly into the chest and opening up the cavity. The blood vessel can then be completely tied off. The incision is then stitched up completely. It is fairly invasive but cats tend to stop showing outward signs of pain after 1 or 2 days post operation. 

For this procedure, an incision is made in the hind leg and a catheter is used to release a small mechanism that will create a blood clot where the blood vessel is supposed to be sealed off. Specialized equipment is needed for this operation and it may not be possible to perform on kittens who are very small. It is minimally invasive and often only requires one day of hospitalization.

As treatment can involve major surgery, it will be necessary to follow all at-home care instructions closely. Ensure that any chest wraps or bandages stay dry and clean throughout the healing process. The incision should be checked daily to ensure that no signs of infection are developing. Do not allow the cat to chew or scratch at the incision site. All activity should be limited during this time. You will need to bring the cat back to the veterinarian in one to two weeks for stitches to be removed. 

If the surgery has been performed correctly and the cat has made a full recovery, most cats will go on to live a long and normal life. An echocardiogram will be needed in the 1-3 months that follow the surgery to ensure heart and lung function have been restored. Regular check-ups will be needed if the heart has undergone permanent damage and long term medication is needed. Cats that have been diagnosed with patent ductus arteriosus should not be bred, to stop the genetic defect from passing on to other cats.