SYMPTOM
Open-mouth breathing
Breathing through the mouth at rest in cats, which differs from normal feline breathing patterns and warrants attention.
Respiratory
Open-mouth breathing in cats and dogs can reflect compromise within the upper or lower airways. Conditions affecting the nasal passages, larynx, trachea, or lung tissue may reduce the efficiency of normal nasal breathing, prompting the animal to breathe through the mouth as an alternative route. The pattern and timing of onset can vary considerably depending on which part of the respiratory tract is involved, and whether the underlying process is inflammatory, structural, or related to fluid accumulation.
Cardiovascular
The heart and lungs function as an integrated system, and when cardiac output is compromised or fluid begins to accumulate in or around the lungs, breathing effort may increase noticeably. Open-mouth breathing can sometimes be one of the more visible signs of cardiovascular strain, particularly in cats where respiratory distress may develop with relatively little warning. The degree of mouth breathing may fluctuate with activity level, body position, and ambient temperature.
Stress and Anxiety
In dogs particularly, open-mouth breathing may be associated with heightened emotional states including anxiety, fear, or excitement. Panting is a normal thermoregulatory behaviour in dogs, but when it occurs in cool environments or during rest without obvious physical exertion, it may reflect underlying psychological distress. Distinguishing between stress-related and physiological causes often requires consideration of the broader context and accompanying behavioural changes.
Metabolic and Systemic
Systemic conditions that alter blood chemistry, such as metabolic acidosis, anaemia, or endocrine disorders, can drive increased respiratory effort as the body attempts to compensate. Open-mouth breathing in these contexts may represent the body's attempt to increase oxygen delivery or adjust carbon dioxide levels. These metabolic drivers can sometimes be subtle, with respiratory changes developing gradually over days or weeks before becoming clearly apparent.
Pain
Acute or chronic pain from various sources can manifest as altered breathing patterns, including open-mouth breathing. Thoracic pain, abdominal discomfort, or musculoskeletal pain may all influence how an animal breathes. In some cases, the pain itself restricts normal chest wall movement, while in others the sympathetic nervous system response to pain drives faster, shallower breathing patterns that may involve the mouth.
Thermoregulatory
Dogs rely heavily on panting as their primary mechanism for dissipating excess body heat, and open-mouth breathing is entirely normal following exercise or in warm environments. However, when this behaviour occurs at rest in comfortable temperatures, or persists well beyond the expected recovery period after exertion, it may warrant closer attention. Cats rarely pant under normal circumstances, so open-mouth breathing in felines tends to carry greater clinical significance regardless of the environmental context.
Why timing matters
Early observation
When open-mouth breathing first appears, it may represent a transient response to a temporary stressor such as heat, exertion, or a brief anxiety-provoking event. In many cases, particularly in dogs, early episodes resolve quickly once the triggering factor is removed. However, the species context matters considerably — in cats, even brief episodes of open-mouth breathing are generally considered more significant because cats do not normally use mouth breathing for thermoregulation. Early episodes that resolve spontaneously may still provide useful information about an animal's developing health picture, particularly if they begin to recur with increasing frequency or appear in contexts where they previously did not occur.
Later presentation
As open-mouth breathing becomes more frequent, prolonged, or occurs with diminishing provocation, the picture may shift. Animals that previously only breathed through their mouths during vigorous exercise may begin to do so during mild activity or even at rest. The breathing pattern itself may also change over time, potentially becoming more laboured, involving visible abdominal effort, or accompanied by audible sounds. In cats, persistent or worsening open-mouth breathing can sometimes indicate progressive compromise of respiratory or cardiac function that may develop more rapidly than in dogs.
The trajectory of open-mouth breathing varies enormously depending on its underlying cause. Stress-related episodes may wax and wane with environmental triggers, while those driven by progressive organ disease may show a more consistent pattern of gradual worsening. Some conditions produce episodic open-mouth breathing interspersed with entirely normal periods, which can make the pattern difficult to characterise without careful observation over time. Recording when episodes occur, their duration, what preceded them, and any accompanying signs can help build a clearer picture of how the breathing pattern is evolving.
Conditions commonly associated
Feline Asthma
Hypertrophic Cardiomyopathy in Cats
Cats with hypertrophic cardiomyopathy may resort to open-mouth breathing when congestive heart failure causes pulmonary oedema and respiratory compromise.
Chronic Upper Respiratory Disease in Cats
Chronic upper respiratory disease with nasal obstruction may force cats to breathe through their mouths, particularly during exertion or stress.
When to explore further
Open-mouth breathing that occurs at rest in a comfortable environment, particularly in cats, may indicate that the body's respiratory demands are not being met through normal nasal breathing. This pattern is considered more clinically relevant than mouth breathing that occurs only during or immediately after physical exertion, as it suggests the respiratory system may be working harder than expected even under minimal physiological demand.
Episodes that are accompanied by other visible changes such as extended neck posture, flared nostrils, visible rib movement during breathing, or a reluctance to lie down may suggest that the animal is actively working to maximise airflow. These postural adaptations are sometimes adopted instinctively to open the airways as widely as possible, and their presence alongside open-mouth breathing can provide additional context about the degree of respiratory effort involved.
When open-mouth breathing develops suddenly in an animal that has not recently been exercising or exposed to heat, the acute onset itself can be informative. Rapid-onset respiratory changes may reflect different underlying processes compared with gradually developing patterns, and the speed of onset may influence how the situation is assessed and what information is most useful to gather.
Changes in the colour of the gums or tongue during episodes of open-mouth breathing can provide important information about oxygen delivery. Bluish, greyish, or unusually pale mucous membranes during breathing episodes may indicate that oxygen exchange is significantly compromised, representing a notable change from the normal pink colour that reflects adequate oxygenation.
Open-mouth breathing that worsens at night or when the animal is lying in certain positions may suggest that body position is influencing airflow or the distribution of fluid within the chest. Some animals may adopt unusual sleeping positions or avoid lying flat altogether, which can itself be an informative observation when considered alongside the breathing pattern.
Observing the broader context around episodes of open-mouth breathing can help build a more complete picture over time. Noting environmental conditions, activity levels, time of day, duration of episodes, and any other changes in behaviour or appetite can all contribute useful information. Video recordings of breathing episodes can be particularly valuable, as they capture details that may be difficult to describe verbally and preserve a record of the breathing pattern at a specific point in time. Understanding the pattern as it develops allows for more informed conversations about what might be contributing to the changes observed.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS