CONDITION
Endocarditis
Endocarditis is an infection of the inner lining of the heart, most often affecting the heart valves. Bacteria that enter the bloodstream—sometimes from the mouth, skin, or urinary tract—can settle on valve tissue and begin to multiply, forming fragile clumps that interfere with the valve's ability to close properly. Over time, this can disrupt normal blood flow and allow pieces of infected material to break away and travel elsewhere in the body. Owners often notice vague signs that build gradually: a dog or cat may seem quieter than usual, lose interest in food, or run a fever that comes and goes. Some animals develop a new heart murmur, while others show signs related to complications—lameness if a clot affects a limb, or breathing changes if the heart begins to struggle. The picture can be subtle at first, and the path to recognising endocarditis often involves piecing together scattered clues. This page explores the patterns that may prompt investigation, the mechanisms by which infection takes hold in the heart, the ways the condition is identified, and the approaches used to manage it. Each section is designed to help you understand what may be happening and what the options look like, without prescribing a single course.
Why this matters now
Endocarditis can appear at any age, but tends to be recognised more often in middle-aged to older dogs, particularly medium and large breeds. Male dogs appear over-represented in many reported case series, though the reasons for this pattern remain unclear. Conditions that allow bacteria to enter the bloodstream—dental disease, skin infections, prostate infections, or procedures that break the skin barrier—may create opportunities for bacteria to reach the heart valves. In cats, endocarditis is diagnosed far less frequently, and the triggering events are often harder to identify.
The infection typically builds over weeks to months, not days. Early on, signs may be so mild or intermittent that they are attributed to something else—a passing upset, minor illness, or simply getting older. As the valve tissue becomes progressively damaged, signs related to poor valve function or embolic events—where fragments of infected material break away and lodge elsewhere—may emerge. The pace varies considerably between individuals; some animals deteriorate relatively quickly once the infection is established, while others follow a slower, more cryptic course.
Signals & patterns
Early signals
Intermittent low-grade fever
The dog or cat may feel warmer to the touch at times, or seem listless for a day or two before appearing to recover. These episodes can be easy to miss, particularly if the animal is otherwise eating and moving normally.
Reduced appetite and weight loss
Food intake may drop gradually, with the animal turning away from meals or eating only small amounts. Over several weeks, this can lead to noticeable weight loss, though the change may be subtle day to day.
Quieter demeanour
The animal may spend more time resting, be less enthusiastic about walks or play, or seem generally less engaged. This shift in energy can be gradual enough that it is attributed to age or weather rather than illness.
Occasional lameness or stiffness
A limb may appear sore or swollen for a brief period, sometimes shifting from one leg to another. This can reflect septic emboli—fragments of infected material that travel to joints or muscles—though the connection is rarely obvious at first.
Later signals
New or changing heart murmur
As the valve tissue becomes increasingly damaged and fails to close properly, turbulent blood flow may produce a sound audible through a stethoscope. This may be detected during a routine examination prompted by other signs.
Breathing changes
If the heart's ability to pump efficiently declines, fluid may begin to accumulate in or around the lungs, leading to faster or more laboured breathing, particularly after mild exertion or when lying down.
Weakness or collapse episodes
As cardiac output falls or emboli affect the brain or other vital organs, the animal may become unsteady, collapse briefly, or seem confused. These episodes may be isolated at first, then recur with increasing frequency.
Click to read about the biological mechanisms
How this is usually investigated
Options & trade-offs
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