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Contact Information

Phone:  919.513.6694
Fax:      919.513.6712
Hours: Monday-Friday, 8AM-5PM
Appointments by referral only, except for second opinions, breed-related certifications for congenital heart disease or treatment of heartworm infection.

General Information

The Terry Center

red Cross Cadeceus

Emergency Service

Main Number: 919.513.6500
Small Animal Emergency: 919.513.6911
Large Animal Emergency: 919.513.6630
Monday-Thursday 5PM-8AM
Friday 5PM-Monday 8AM

Open 24 hours on legal holidays.
No appointment needed.

Cardiology - Heart Failure

What is heart failure?

Heart failure means that the heart has lost the ability to pump enough blood through the body to meet the body's needs. Usually, the loss in pumping action is a symptom of an underlying heart problem, such as chronic valvular heart disease (defined below).

Although the term heart failure may sound like the heart suddenly stopped beating, heart failure usually develops slowly - often even over years, as the heart gradually loses its pumping ability and works less efficiently.

The severity of heart failure depends on how much pumping capacity the heart has lost, and what disease or process has caused the loss. Animals generally lose some pumping capacity as they age, but in companion animals (dogs and cats) heart failure is rare unless some disease process severely damages either the heart valves or the heart muscle.

At one end of the severity spectrum, early chronic valvular disease, some forms of hypertrophic cardiomyopathy and some mild congenital heart defects may have little effect on an animal's lifestyle or life expectancy; at the other end, severe heart failure can interfere with even simple activities and prove rapidly fatal. Between those extremes, treatment can often help pets lead full lives. Heart failure is always a serious health problem that deserves prompt and precise diagnosis, as most causes of heart failure require medical treatment.

The term congestive heart failure is often used to describe all patients with heart failure. In reality, congestion (the buildup of fluid) is just one feature of the condition and does not occur in all patients. There are two main categories of heart failure, although within each category, symptoms and effects may differ from patient to patient. The two categories are:

Frequently Asked Questions about Heart Failure

What causes heart failure?

In dogs, the most common causes are chronic degenerative heart valve disease (in small dogs), and dilated primary heart muscle disease (cardiomyopathy) in large dogs. In cats, hypertrophic primary heart muscle disease (cardiomyopathy) is most common. Heart valves are thin, flap-like structures that help regulate blood flow through the heart. Infections in the heart are another source of increased risk for heart failure, but this is uncommon. In both dogs and cats, concurrent diseases of other organ systems such as hypertension (high blood pressure) and hyperthyroidism may be important contributors to heart disease, especially in older pets. Finally, genetic abnormalities contribute to the risk for certain types of heart disease, which in turn may lead to heart failure. However, in most instances, a specific genetic link to heart failure has not been identified.

What are the symptoms?

A number of symptoms are associated with heart failure, but none is specific for the condition. Perhaps the best known symptom is shortness of breath ("dyspnea"). In heart failure, this may result from excess fluid either in or around the lungs. The breathing difficulties may occur at rest or during exercise. In some cases, congestion may be severe enough to prevent or interrupt sleep. Persistent coughing is another common sign of heart failure, especially in smaller dogs.

Fatigue or easily tiring is another common symptom. As the heart's pumping capacity decreases, muscles and other tissues receive less oxygen and nutrition, which are carried in the blood. Without proper "fuel," the body cannot perform as much work, which translates into fatigue and lethargy.

Fluid accumulation may distend the abdomen. Excess fluid retained by the body may result in weight gain, which sometimes occurs fairly quickly. Muscle mass in these animals, however, is nearly always decreased.

Because heart failure usually develops slowly, the symptoms may not appear until the condition has progressed to an advanced state. The heart "hides" the underlying problem by making adjustments that delay - but do not prevent - the eventual loss in pumping capacity. The heart adjusts, or compensates, in three ways to cope with and hide the effects of heart failure:

By making these adjustments, or compensating, the heart can temporarily make up for losses in pumping ability, sometimes for years. Compensation has its limits, however, and eventually the signs of heart failure appear.

How do veterinarians diagnose heart failure?

In many cases, veterinarians diagnose heart failure during a physical examination. Readily identifiable signs are shortness of breath, fatigue, combined with clues from listening to the heart and chest. The veterinarian usually will recommend a variety of further diagnostic tests. Chest radiographs (x-rays) can determine the heart's size and shape, and are used to evaluate the presence of lung congestion or disease, as well. An electrocardiogram is a recording device used to evaluate the electrical activity of a patient's heartbeat, allowing the veterinarian to closely monitor the heart rate and determine whether any heart rhythm abnormalities are present.

Echocardiography is another means of evaluating heart structure and function from outside the body. High frequency sound waves are beamed into the heart and their reflections are recorded and translated into images. The pictures reveal the shape and size of the heart's chambers, and allow evaluation of the valves. Echocardiography is used to calculate various measurements of how well the heart is able to contract and relax.

Laboratory tests help rule out other possible causes of symptoms, including conditions that might overload the heart such as severe anemia and hyperthyroidism (a disease resulting from an overactive thyroid gland). In general, the patient's blood pressure will also be measured.

What treatments are available?

If heart failure is being caused by excessive work, it can often be cured if the primary cause of the excessive work can be removed (such as severe anemia or hyperthyroidism or hypertension). Some anatomical problems, such as congenital (present from birth) defects, can be corrected either surgically or by catheter based intervention.

The most common causes of heart failure - those due to damaged heart valves or muscle, are usually not curable. Treatment for these forms may, however, be quite successful. Treatment seeks to improve the patient's quality of life and length of survival – generally through drug therapy along with certain "lifestyle" changes (diet and exercise). Many patients need to receive three or more medications.

Several types of drugs have proven useful in the treatment of heart failure:

Common Heart Failure Medications

Listed below are some of the medications prescribed for heart failure. Not all medications are suitable for all patients, and more than one drug may be needed.

To improve the chances of the pet surviving with heart failure, owner's should:

What is the outlook for heart failure?

Even with the best care, heart failure can worsen. Most veterinary patients that have been in heart failure eventually die of their heart disease. Within the past decade, knowledge of heart failure has improved dramatically but much more remains to be learned. The NCSU Cardiology Service supports numerous research projects aimed at building on what is already known about heart failure and at uncovering new knowledge about its causes, diagnosis and treatment.


Angiotensin converting enzyme (ACE) inhibitor - A drug used to decrease pressure inside blood vessels.

Arrhythmia - An irregular heartbeat.

Congestive heart failure - A heart disease condition that involves loss of pumping ability by the heart, generally accompanied by fluid accumulation in body tissues, especially the lungs.

Diastolic heart failure - Inability of the heart to relax properly and fill with blood as a result of stiffening of the heart muscle.

Dyspnea - Shortness of breath.

Echocardiography - Recording sound waves bounced off the heart to produce images of the heart.

Edema - Abnormal fluid accumulation in body tissues.

Electrocardiogram (EKG or ECG) - Measurement of electrical activity associated with heartbeats.

Heart failure - Loss of blood-pumping ability by the heart.

Pleural effusion - Fluid accumulation around the lungs (in the chest cavity).

Pulmonary congestion (or edema) - Fluid accumulation in the lungs.

Sudden cardiac death - Cardiac arrest caused by an irregular heartbeat.

Systolic heart failure - Inability of the heart to contract with enough force to pump adequate amounts of blood through the body.

Valves - Flap-like structures that control the direction of blood flow through the heart.