When to see a vet urgently
Deterioration with suspected endocarditis may require emergency care. Contact a vet immediately if:
- your cat struggles to breathe or breathes with its mouth open at rest;
- it collapses, is extremely weak or has very pale or bluish mucous membranes;
- a limb suddenly becomes painful, cold or weak;
- fever or suspected infection accompanies rapidly deteriorating condition and refusal of food.
Do not wait for a specialist appointment if breathing or circulation is unstable. You can find a vet near you.
Overview
Endocarditis develops when bacteria, or less often fungi, enter the bloodstream and attach to heart valves. Inflammation destroys and distorts valves, disrupting cardiac function. In cats, it often complicates sepsis, chronic infections or serious injuries and surgery.
An infected valve can develop a growth-like deposit called a vegetation, containing inflammatory material, clot and microbes. The valve may no longer close normally, allowing blood to flow backwards. Commonly described feline sites include the mitral and aortic valves. The workload caused by valve dysfunction may therefore need treatment alongside infection.
Bacteraemia and sepsis differ. Bacteraemia means bacteria are in the bloodstream. Sepsis is a life-threatening, abnormal response to infection involving organ dysfunction. Fever or raised inflammatory markers alone do not confirm either sepsis or endocarditis. Nevertheless, a patient with endocarditis also needs assessment for systemic infection consequences.
Causes
- Bacteraemia, with bacteria entering blood from an infection site.
- Bartonella, flea-borne bacteria associated with endocarditis and myocarditis in cats, although endocarditis overall is uncommon.
- Pus-forming infections, including abscesses, pyometra and cellulitis.
- Chronic oral infections, including stomatitis and periodontitis.
- Postoperative complications.
- Intravenous catheters and prolonged fluid therapy, rarely.
A possible source needs investigation, but the origin in an individual cat may remain unknown. Surgery, dental disease or a catheter cannot be identified as the cause from timing alone. Detecting a valve lesion and investigating microbes are separate tasks. Bacteria other than Bartonella may also be responsible.
Bartonella tests need careful interpretation because many infected cats have no symptoms. A positive antibody or blood PCR result alone therefore does not show that this bacterium is damaging a valve. The vet interprets it alongside cardiac findings, other tests and alternative diagnoses.
Risk factors
- Elderly cats.
- Cats with chronic inflammatory diseases.
- Cats with weakened immunity through FIV or FeLV.
- Cats after serious injuries or surgery.
Research on feline endocarditis is limited, so individual risk factors are not precisely understood. Cases also occur in younger cats, and breed or sex alone does not determine risk. FeLV or FIV infection does not in itself confirm endocarditis either.
Typical symptoms
Feline endocarditis can cause:
- lethargy and reduced activity;
- fever with sepsis;
- rapid breathing and breathlessness;
- arrhythmias and heart murmurs;
- coughing when fluid accumulates in the lungs;
- weight loss and refusal of food;
- possible arterial blockage signs, including hindleg paralysis.
Early signs may be vague. Lameness or reluctance to move can reflect systemic infection effects, an inflammatory joint problem or blocked circulation. Examination of a feverish, lame cat therefore extends beyond the painful leg. A suddenly cold, paralysed limb is especially urgent.
Coughing is not typical of feline heart failure. Do not automatically explain it through endocarditis; airway diseases need consideration too. Rapid or laboured breathing can reflect fluid accumulation, but its cause also needs investigation. A symptom list cannot provide a reliable home diagnosis.
Complications and consequences
- Chronic heart failure.
- Valve vegetations and destruction.
- Arterial blockages affecting limbs, brain or kidneys.
- Sepsis.
- Death.
Infection can permanently damage a valve even if microbes are later controlled. Material can also break from vegetations into circulation, causing blockages or infections elsewhere. Monitoring therefore assesses cardiac function and organs such as the kidneys. Deterioration does not always mean only continuing local valve infection.
Diagnosis at the vet
- Listening for murmurs and arrhythmias.
- An ECG to identify rhythm disturbances.
- Heart ultrasound to assess valve thickening, vegetations and abnormal blood flow.
- Blood tests for increased white cells and inflammatory markers.
- Blood culture.
How is suspicion confirmed?
Ultrasound looks for irregular valves, vegetations and leakage. A murmur alone does not identify its cause. ECG helps identify an arrhythmia but cannot alone demonstrate valve infection. Chest imaging may be needed for suspected pulmonary oedema or another cause of breathing difficulty.
Diagnosis combines the results. Inflammatory blood changes support suspicion but do not identify the infected valve or organism. A first ultrasound does not always settle the question either. Changes in condition or listening findings may justify repeating it, as valve lesions can develop during the illness.
Blood culture and other microbial tests
Blood culture aims to identify bloodstream bacteria and their antibiotic susceptibility. Samples are taken before antibiotics when possible. The vet arranges aseptic collection and decides which samples are needed. Report treatment already started and every previous antibiotic, as these affect interpretation.
A negative culture does not always exclude infection. Some organisms require special tests, and sample quality and handling affect findings. Suspected Bartonella may need molecular methods and serology alongside culture. Conversely, a single positive result must be distinguished from contamination or a finding unrelated to the cardiac lesion.
Treatment and follow-up
Treating infection and complications
Endocarditis usually requires prolonged antibiotic treatment planned by a vet. The medicine is chosen from the identified organism and susceptibility results when possible. Treatment of a very sick cat may begin before final results and be refined later. This does not make samples unnecessary or trying leftover medicines at home safe.
Antibiotics alone do not correct heart failure, valve damage or arterial blockage. A breathless cat may need hospitalisation, oxygen and treatment targeting fluid accumulation. Fluid in the chest cavity may require drainage. Pain relief and nutritional support are also assessed. Fluids are tailored to circulation and the heart's ability to tolerate them.
Monitoring includes general condition, blood tests and cardiac findings. Falling fever or temporary improvement alone does not establish that a valve infection has cleared. Check-ups assess infection control, possible new organ damage and medication safety. You receive administration instructions and guidance on signs requiring contact before the planned appointment.
Home monitoring and prognosis
Watch breathing during quiet rest or sleep without purring. Record appetite, activity and any lameness. These observations help the vet compare condition over time. Laboured breathing or a suddenly painful, weak limb requires emergency contact regardless of measurements.
Maintaining food intake and muscle condition matters in heart disease. Diet is tailored to disease stage and other illnesses, rather than severely restricted yourself. Explain if your cat refuses food used for medicines and therefore misses medication.
Prognosis is often poor because many cats are diagnosed after cardiac function has deteriorated. Nevertheless, one patient's outlook is not determined from average survival in a case series. Valve damage, infection control, complications and response all matter. Goals and quality of life are reassessed during follow-up.
Prevention
- Treat oral, skin and internal organ infections promptly.
- Treat and monitor chronic inflammation.
- Use careful asepsis for catheter placement and surgery.
- Arrange regular reviews for cats with heart disease.
- Maintain flea control to prevent Bartonella transmission.
Flea control reduces Bartonella transmission risk but does not eliminate endocarditis caused by other bacteria. Treating mouth and skin inflammation matters for health, but not every such infection reaches the heart. A symptom-free cat does not need an endocarditis diagnosis or antibiotics from flea exposure alone.
Important for cat owners
Endocarditis is an uncommon but extremely serious, life-threatening feline disease. Remember that breathlessness, lethargy, weight loss and heart murmurs are serious findings requiring assessment by a vet experienced in heart disease. Only early diagnosis and infection treatment can slow progression and improve prognosis.
This article provides general information and does not replace veterinary care. If you notice signs of illness in your cat, contact a vet.
Frequently asked questions
Does a heart murmur establish endocarditis?
Not alone. A murmur indicates abnormal blood flow and has many possible causes. Suspected endocarditis is assessed through heart ultrasound, clinical findings and infection tests together.
Is endocarditis possible with a negative blood culture?
Yes. Routine culture does not detect every organism, and previous medication or sample handling can affect results. The vet assesses further testing needs alongside other findings.
Can treatment stop when my cat seems brighter?
Not on your own decision. Symptom improvement alone does not confirm elimination of valve infection. Check-ups determine continued treatment and changes, while also assessing cardiac function and medication safety.
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
- Infective endocarditis in 13 cats, Journal of Veterinary Cardiology / PubMed, accessed 2026-11-05.
- Endocarditis in Cats, VCA Animal Hospitals, accessed 2026-11-05.
- Clinical cases of infectious endocarditis in cats, Brazilian Journal of Veterinary Medicine / PubMed Central, accessed 2026-11-05.
- GUIDELINE for Feline bartonellosis, ABCD, accessed 2026-11-05.
- Microbiology Testing for Animals, Merck Veterinary Manual, accessed 2026-11-05.
- Sepsis in Dogs and Cats—Consensus Definition and Clinical Criteria, Journal of Veterinary Emergency and Critical Care, accessed 2026-11-05.
- Congestive Heart Failure in Cats, VCA Animal Hospitals, accessed 2026-11-05.
- Coughing in Cats, VCA, accessed 2026-11-05.
- Home Breathing Rate Evaluation, VCA Animal Hospitals, accessed 2026-11-05.
- Heart Disease – Nutrition, Tufts University Cummings School of Veterinary Medicine, accessed 2026-11-05.