CONDITION
Mitral Valve Disease in Dogs
Why this matters now
Mitral valve disease is the most common acquired cardiac condition in dogs, particularly prevalent in small to medium breeds from middle age onward. Cavalier King Charles Spaniels, Dachshunds, Miniature and Toy Poodles, Chihuahuas, and other small breeds carry a notably higher predisposition, with some studies suggesting that the majority of Cavaliers develop some degree of mitral valve degeneration by mid-life. The condition is a progressive degenerative process rather than a sudden event — the valve leaflets gradually thicken, distort, and lose their ability to form a tight seal when the heart contracts. Because of this gradual onset, many dogs live with early-stage disease for years without showing any outward signs, and the condition may first be identified incidentally during a routine examination when a heart murmur is detected. The prevalence increases markedly with age, and in the overall canine population it represents one of the most significant cardiac conditions encountered.
The progression of mitral valve disease follows a broadly predictable trajectory, though the speed varies considerably between individual dogs. Initially, the valve leaks a small amount of blood backward into the left atrium with each heartbeat — a stage that may produce no clinical signs and can remain stable for months or years. As the degeneration advances, the volume of regurgitant blood increases, and the heart compensates by enlarging to accommodate the extra workload. This compensatory phase may be prolonged, with the heart maintaining adequate function despite progressive structural changes. Eventually, the compensatory mechanisms become insufficient, and the heart can no longer maintain adequate forward blood flow while managing the regurgitant volume. This decompensation marks the transition to congestive heart failure, where fluid accumulates in the lungs, producing coughing, increased breathing effort, and exercise intolerance. Some dogs experience sudden deterioration due to chordae tendineae rupture — the snapping of the cord-like structures that anchor the valve leaflets — which can cause an abrupt worsening of the regurgitation.
Signals & patterns
Early signals
Heart murmur detected on examination
A heart murmur is often the earliest detectable sign of mitral valve disease, identified by a veterinarian during auscultation with a stethoscope. The murmur is typically heard best on the left side of the chest and may initially be soft (low grade), becoming louder as the disease progresses and the volume of regurgitant blood increases. Many dogs with early murmurs show no other signs and appear completely normal at home.
Subtle exercise intolerance
Owners may notice that their dog tires slightly more easily during walks or play sessions, or that recovery time after exertion seems longer than it once was. In small breeds, this can be difficult to distinguish from normal ageing or the dog's established activity preferences. The reduced exercise tolerance reflects the heart's gradually diminishing ability to increase its output during periods of increased demand.
Intermittent coughing
A mild, intermittent cough may develop, particularly at night or in the early morning hours when the dog has been lying down. This early cough may be attributed to other causes such as tracheal irritation or kennel cough before its cardiac origin is recognised. The cough may initially be dry and nonproductive, occurring a few times a day, and may be more noticeable after exercise or excitement.
Mildly increased resting respiratory rate
A subtle increase in the number of breaths taken per minute while resting or sleeping may be one of the earliest indicators of fluid beginning to accumulate. Normal resting respiratory rates for dogs are typically below 30 breaths per minute, and consistent readings above this level during relaxed sleep can provide early warning of developing congestion before more obvious signs appear.
Later signals
Persistent cough and breathing difficulty
As heart failure develops, coughing becomes more frequent, persistent, and may become productive with frothy or blood-tinged sputum in advanced cases. The dog may show increased breathing effort with visible abdominal movements during respiration, particularly when lying down. Some dogs develop a preference for sleeping with their chest elevated or may resist lying down entirely, as the recumbent position worsens pulmonary congestion.
Abdominal distension
In cases where the right side of the heart also becomes affected, or in advanced left-sided failure, fluid may accumulate in the abdominal cavity (ascites). This produces a gradual swelling of the abdomen that may initially be mistaken for weight gain. The abdomen may feel fluid-filled when gently pressed, and the dog may show discomfort when the belly is touched.
Fainting episodes
Syncope — brief episodes of collapse or fainting — may occur, particularly during excitement, exertion, or coughing fits. These episodes typically last seconds to a minute and the dog usually recovers quickly afterward. They result from momentary inadequacy of blood flow to the brain, often triggered by arrhythmias or sudden drops in blood pressure associated with the diseased valve.
Marked weight and muscle loss
Cardiac cachexia — the progressive loss of muscle mass and body condition associated with chronic heart disease — may develop in advanced stages. The dog may lose weight despite maintaining or even increasing its food intake. The muscle wasting may be particularly noticeable over the spine, hips, and temporal muscles of the head, sometimes masked by concurrent fluid retention in other body regions.
Click to read about the biological mechanisms
How this is usually investigated
The investigation of mitral valve disease typically begins with the detection of a heart murmur and progresses through a series of assessments designed to characterise the severity of the valve degeneration, the degree of cardiac remodelling, and whether heart failure has developed. The staging of the disease guides the approach to monitoring and management, with each stage carrying different implications for the dog's current wellbeing and future trajectory.
Thoracic radiography (chest X-rays)
Echocardiography (cardiac ultrasound)
Electrocardiography (ECG)
Blood pressure measurement
Blood and urine testing
Options & trade-offs
The management of mitral valve disease depends on the stage of the disease and whether congestive heart failure has developed. Approaches range from monitoring alone in early stages to multi-drug protocols in advanced heart failure. Each approach involves considerations about efficacy, side effects, monitoring requirements, and quality of life implications that inform individual management decisions.
Monitoring and lifestyle support (preclinical stage)
Dogs with early mitral valve disease that have not yet developed heart enlargement or clinical signs may be managed with regular monitoring to track disease progression. This typically involves periodic veterinary examinations, radiographs, and/or echocardiography at intervals determined by the disease stage. Maintaining an appropriate body weight, providing moderate exercise as tolerated, and monitoring resting respiratory rate at home can all contribute to early detection of progression.
Trade-offs: The primary consideration in the monitoring phase is determining the appropriate frequency and intensity of reassessment. Too-infrequent monitoring risks missing the transition point where intervention may be beneficial, while very frequent assessments increase cost and stress without changing the outcome if the disease remains stable. The balance depends on the rate of progression observed in the individual dog.
Pimobendan therapy (preclinical with cardiomegaly)
For dogs that have developed significant cardiac enlargement but have not yet shown clinical signs of heart failure, pimobendan — a positive inotrope and vasodilator — may be introduced. This medication strengthens the heart's contraction while reducing the resistance against which it pumps, and has been shown in large clinical trials to delay the onset of congestive heart failure in dogs with preclinical mitral valve disease and cardiomegaly.
Trade-offs: Pimobendan requires accurate staging to determine the appropriate point of initiation, typically guided by echocardiographic measurements of left atrial and ventricular size. It is generally well tolerated but requires ongoing monitoring. The decision to initiate pimobendan in the preclinical stage involves weighing the evidence for delayed progression against the commitment to long-term daily medication.
Multi-drug heart failure management
Once congestive heart failure develops, management typically involves a combination of medications including diuretics (most commonly furosemide) to reduce fluid accumulation, pimobendan to support cardiac function, and ACE inhibitors to counteract the neurohormonal activation driving disease progression. Additional medications such as spironolactone may be added as the disease advances. The goal is to control clinical signs, maintain comfort, and slow the progression of the disease.
Trade-offs: Multi-drug protocols require careful dose titration and regular monitoring of kidney function and electrolytes, as diuretics in particular can affect kidney perfusion and electrolyte balance. The frequency of monitoring and medication adjustments tends to increase as the disease progresses. Balancing effective fluid control against the potential for excessive dehydration and kidney compromise is an ongoing consideration. Quality of life assessment becomes an increasingly central part of management decisions.
Surgical mitral valve repair
Surgical repair of the mitral valve is a specialised procedure available at a limited number of veterinary centres worldwide. The surgery involves repairing or replacing the degenerated valve leaflets and chordae tendineae under cardiopulmonary bypass, aiming to restore competent valve closure and eliminate or dramatically reduce regurgitation. When successful, surgical repair can transform the disease trajectory, potentially offering long-term resolution of the valve dysfunction.
Trade-offs: Mitral valve surgery carries significant perioperative risk and requires highly specialised surgical and anaesthetic expertise. It involves substantial financial commitment and a period of intensive postoperative care. The availability of centres performing this procedure is limited. When performed successfully by experienced teams, outcomes can be excellent, but the procedure is not without complications and careful patient selection is important. The decision to pursue surgical repair involves weighing the potential benefits against the procedural risks, costs, and the availability of experienced surgical teams.
Common misconceptions
"A heart murmur means the dog is in heart failure"
A heart murmur indicates that turbulent blood flow is occurring within the heart, but it does not necessarily mean heart failure is present. Many dogs live for years with a murmur detected on examination without ever developing clinical signs. The murmur indicates the presence of valve disease, but the stage and severity determine whether the dog is currently affected. The progression from detectable murmur to clinical heart failure involves intermediate stages of cardiac remodelling that can be monitored and, at certain points, may benefit from intervention.
"Dogs with heart disease should avoid all exercise"
While intense or prolonged exercise may need to be moderated in dogs with significant cardiac disease, complete exercise restriction is generally not appropriate and can contribute to muscle loss, weight gain, and reduced quality of life. Dogs with preclinical disease typically tolerate moderate exercise well, and even dogs with managed heart failure often benefit from gentle, controlled activity. The key is matching activity levels to the individual dog's tolerance, monitoring for signs of excessive fatigue or breathing difficulty, and adjusting the intensity and duration of exercise as the condition evolves.
"Coughing in a dog with a known heart murmur is always caused by the heart"
While coughing can certainly result from cardiac disease — particularly pulmonary oedema or left atrial enlargement compressing the airway — dogs with heart murmurs can also develop coughs from entirely unrelated causes. Tracheal collapse, chronic bronchitis, respiratory infections, and other airway conditions are common in the same small breed populations that are predisposed to mitral valve disease. Assuming that all coughing in a dog with a murmur is cardiac in origin may delay recognition of concurrent respiratory conditions that require different management approaches.
Monitoring the resting respiratory rate at home — counting the number of breaths per minute while the dog is relaxed or asleep — is one of the most valuable observations an owner can make for a dog with mitral valve disease. Establishing a baseline and noting any consistent upward trend can provide early indication of fluid accumulation in the lungs before other signs become apparent. Keeping a simple log of daily or weekly resting respiratory rates, along with notes about the dog's activity level, appetite, coughing frequency, and general demeanour, creates a longitudinal record that can reveal subtle trends that might otherwise go unnoticed. Understanding the staged nature of the disease — that it progresses through recognisable phases, each with different implications — can help frame expectations and support informed conversations about monitoring and management as the condition evolves over time.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS