When to see a vet urgently
A kitten with a known heart defect or one previously appearing healthy needs immediate help if:
- Breathing is laboured or open-mouthed at rest.
- Mucous membranes become bluish or grey.
- The cat collapses, faints or cannot get up.
- A limb suddenly becomes painful, cold or unable to function.
Limit handling during breathing difficulty and tell the emergency practice you are coming. You can find a vet near you.
Overview
A cat's heart has four chambers, two atria and two ventricles, separated by walls and equipped with valves. Congenital defects can affect the dividing walls, valves or major blood vessels, disrupting blood flow and straining the heart. Depending on the defect, the animal may have no symptoms or a life-threatening condition.
The right side sends blood to the lungs for oxygenation, while the left pumps oxygenated blood around the body. Atria receive blood and ventricles pump it forwards. Dividing walls and valves direct flow appropriately. A small structural abnormality and a large abnormal diversion of blood flow can therefore impose very different demands on circulation.
Main types
- Ventricular septal defect (VSD): a hole in the wall between the ventricles, causing blood to mix.
- Atrial septal defect (ASD): a hole between the atria.
- Aortic or pulmonary stenosis: narrowing of the heart's outflow, increasing the workload on heart muscle.
- Patent ductus arteriosus (PDA): a foetal vessel connecting the pulmonary artery and aorta fails to close after birth.
- Valve abnormalities: underdeveloped or malformed valves.
Hole size and flow direction matter
With a VSD, blood usually flows from the left ventricle into the right. This does not always mean mixing of oxygen-poor and oxygen-rich blood in a way that produces bluish colouration. Hole size and pressure differences between the heart's sides determine how much blood takes the wrong route. A small hole may have little significance, while a large one causes substantial strain.
With PDA, a vascular connection needed during foetal life remains open after birth. The usual shunt from the aorta into the pulmonary artery increases blood returning to the lung circulation. Rarely, severe pulmonary hypertension can reverse the flow. This greatly affects assessment of treatment options.
A valve defect may allow blood to leak backwards. With abnormal mitral valve development, for example, blood may return from the left ventricle to the left atrium. With stenosis, the heart instead needs to generate higher pressure to move blood forwards. Not every defect listed can therefore be treated in the same way.
Causes
The main cause of congenital heart defects is a genetic developmental abnormality. Additional risk factors include:
- inherited susceptibility in certain breeds
- complications during the mother's pregnancy
- effects of toxins, infections or poor nutrition during pregnancy
Congenital means present from birth, but does not automatically mean proven inheritance. Genes and the environment in the womb may act together, and the precise cause of an individual cat's defect may remain unknown. Information on the importance of these risk factors and breed-specific inheritance in cats is limited; canine breed predispositions should not simply be applied to cats. Nor can a particular maternal exposure be identified from a kitten's heart finding alone.
Symptoms
Kittens may have:
- slow growth and poor development
- rapid tiring
- breathlessness and rapid breathing
- pale or bluish mucous membranes
- exercise intolerance
- fainting and, rarely, seizures
- heart murmurs detected on auscultation
At home, you may see a kitten stop playing sooner than others, become breathless with less activity or fall behind in growth. These observations are not specific to heart defects, so other diseases are investigated too. Do not test exercise tolerance by forcing the kitten to play.
A murmur is an abnormal blood-flow sound heard through a vet's stethoscope. It is not a symptom to assess at home. Kittens can also have harmless murmurs, so auscultation alone does not confirm a structural defect.
In some cases, disease remains hidden and is detected only during a scheduled examination or heart ultrasound.
Complications and consequences
Severe defects can lead to:
- chronic heart failure
- delayed kitten development
- sudden death
- increased strain on the lungs and liver
Serious complications are possible, but a small structural defect may be compatible with good quality of life and a normal lifespan. Prognosis is not determined by the defect's name alone. The same cat may also have several structural abnormalities, whose combined effects are assessed.
Veterinary diagnosis
- auscultation to detect heart murmurs
- heart ultrasound, or echocardiography, the main method
- chest X-rays
- an electrocardiogram (ECG)
What does a heart examination investigate?
Ultrasound shows the chambers, dividing walls, valves and their movement. Doppler measurements assess blood-flow direction and speed. This distinguishes, for example, a small septal hole from a large shunt and establishes whether heart chambers show signs of strain. It also helps plan any procedure.
An ECG records electrical heart activity and helps identify arrhythmias. It does not replace ultrasound for structural assessment. Chest X-rays assess factors including heart size and possible fluid changes in the lungs. Stabilising a cat with breathing difficulties may be more important than taking every image immediately.
Describe the kitten's growth, energy and fainting episodes, and known heart defects or sudden deaths in the family. Auscultation assesses a murmur's timing and character as well as loudness. Loudness alone cannot establish how extensive an operation a kitten needs or whether it needs one at all.
Treatment, monitoring and prognosis
Corrective treatment or symptom control?
Some defects can be corrected or the strain they cause reduced through a procedure. Closing an ordinary left-to-right PDA is an example of treatment targeting the structure. Technique and timing depend on anatomy and the cat's condition. Early investigation may allow treatment before permanent damage develops.
However, PDA closure is not suitable for every flow pattern. If severe pulmonary hypertension has reversed flow from right to left, closure can be dangerous. Knowing that the vessel remains open is therefore insufficient for a procedural decision. Options for repairing septal defects and valve abnormalities are assessed separately.
A small defect without symptoms does not always require medication or surgery. Follow-up assesses whether heart size or function changes with growth. With a severe defect, medicines can treat heart failure or arrhythmias, for example, even if the structural abnormality remains. Treatment goals and prognosis are discussed individually.
If heart failure causes breathing difficulties, oxygen and medication reducing fluid accumulation may be needed. Chest fluid may need removal so the lungs can expand. Do not change medication at home without instructions or copy another heart patient's treatment for a kitten.
What should owners monitor?
Watch appetite, growth and energy. Report difficulty eating or avoidance of previous activities. Mention the heart defect before anaesthesia or treatment for another illness so the risk can be considered. Ask for individual advice about suitable activity too.
Monitoring breathing during sleep can help identify a change in condition. Count only during calm sleep without purring and record the result for comparison. Breathing after play or stress is not directly comparable with the sleeping rate. The vet provides an individual contact threshold when needed; visible breathing difficulty is urgent even without counting.
Prevention
Congenital heart defects cannot be completely prevented, but risk may be reduced through:
- not breeding from animals with heart defects
- monitoring the health of pregnant cats
- complete nutrition and vaccinations during pregnancy
- early heart examinations for at-risk kittens
The vaccination point requires qualification: a vet decides on vaccination of a pregnant cat according to the product's safety instructions and infection risk. A live attenuated panleukopenia vaccine is not used in a pregnant cat. Vaccination also cannot correct a structural heart defect that has already developed in a foetus.
Breeding plans consider family history as well as the finding and, when needed, examination of close relatives. A healthy appearance does not replace heart investigation where defects have been identified in the family. There is no single shared genetic test or preventive measure for every congenital heart defect.
What it means for owners
Although congenital heart defects are rare, they need attention. Owners should know:
- at-risk kittens should have heart ultrasound
- suspected disease warrants immediate contact with a veterinary cardiologist
- early diagnosis helps manage the disease course and improves the kitten's quality of life
This material is for information only and does not replace veterinary treatment. If your cat develops symptoms, contact a vet.
Frequently asked questions
Does a kitten's heart murmur always mean a congenital heart defect?
No. A kitten may also have a harmless murmur. Its characteristics, other findings and ultrasound when needed determine further investigation. However, a kitten with symptoms should not be left waiting to see whether the murmur disappears on its own.
Can a cat with a congenital heart defect live normally?
Yes, if the defect is small and causes no significant strain. With severe or several concurrent defects, prognosis may be poor. Heart structure, function and treatment options provide a more accurate assessment than the diagnosis name alone.
Is a congenital heart defect always inherited from the parents?
Not necessarily. Congenital means the defect was present from birth. A genetic contribution may be possible or established, but other developmental influences may also be involved. Breeding from an affected cat is avoided and family history reviewed.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
- Congenital Heart Disorders, Cornell Feline Health Centre, accessed 2026-11-03.
- Congenital and Inherited Disorders of the Cardiovascular System of Cats, Merck Veterinary Manual, accessed 2026-11-03.
- Cardiac Shunts in Animals, Merck Veterinary Manual, accessed 2026-11-03.
- Congenital Heart Disease, University of Illinois College of Veterinary Medicine, accessed 2026-11-03.
- Heart Disease – Cats, Tufts University Cummings School of Veterinary Medicine, accessed 2026-11-03.
- Home Breathing Rate Evaluation, VCA Animal Hospitals, accessed 2026-11-03.
- 2024 guidelines for the vaccination of dogs and cats, World Small Animal Veterinary Association, accessed 2026-11-03.
- Congestive Heart Failure in Cats, VCA Animal Hospitals, accessed 2026-11-03.