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Cardiology: What is Congestive 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:

  • Systolic heart failure: This occurs when the heart’s ability to contract decreases. Either the heart muscle cannot pump with enough force, or a leaking valve prevents it from pushing a sufficient amount of blood into the circulation. Blood coming into the heart from the lungs may back up and cause fluid to leak into the lungs, a condition known as pulmonary (lung) congestion or edema. Blood coming back to the right side of the heart may also back up in the great veins, causing fluid to accumulate in the chest or abdomen.
  • Diastolic heart failure: This occurs when the heart muscle has a problem relaxing. The heart cannot properly fill with blood because the muscle has become stiff, losing its ability to relax. This form may also lead to fluid accumulation, especially in the chest in cats. Some patients may have lung congestion and edema.

Frequently Asked Questions about 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.

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:

  • Enlargement (“dilatation”), which allows more blood into the heart;
  • Thickening of muscle fibers (“hypertrophy”) to strengthen the heart muscle, which allows the heart to contract more forcefully and pump more blood; and
  • More frequent contraction (increased heart rate), which increases circulation.

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.

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.

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:

  • Diuretics help reduce the amount of fluid in the body and are useful for patients with fluid retention.
  • Several clinical studies have shown that angiotensin converting enzyme (ACE) inhibitors improve survival among heart failure patients and may slow the loss of heart function. Other drugs that inhibit the renin-angiotensin-aldosterone system may also be useful.
  • Digitalis often helps improve circulation.
  • Beta adrenergic blockers (drugs that block the effects of the sympathetic or “fight or flight” nervous system) may also prolong survival and help regulate the heart rhythm.

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.

  • ACE Inhibitors – prevent the production of a chemical that causes blood vessels to narrow. As a result, blood pressure drops and the heart does not have to work as hard to pump blood. Side effects are rare, but the primary veterinarian will need to check the patient’s renal function and electrolytes 3–7 days after starting therapy.
  • Digitalis – Slows the heart rate in some arrhythmias and increases the force of the heart’s contractions. As a result, the heart beats less frequently but more effectively, and more blood is pumped into the arteries. Side effects may include loss of appetite, vomiting, diarrhea, and new heartbeat irregularities. The primary veterinarian will need to check the blood level of digitalis 3 – 7 days after starting therapy – ideal levels are between 0.5 – 1.5 ng/ml of digoxin.
  • Diuretics – Decrease the retention of salt and water. Diuretics come in many types, with different periods of effectiveness. Side effects may include weakness, loss of appetite, and electrolyte disturbance. If the patient is breathing comfortably but loses appetite or vomits, the owner should contact their primary veterinarian and discontinue diuretic administration until they have been consulted.
  • Hydralazine — widens blood vessels, easing blood flow. Side effects may include weakness, low blood pressure, rapid heartbeat.
  • Amlodipine – widens blood vessels, easing blood flow. Side effects may include weakness, low blood pressure, rapid heartbeat.

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

  • See their primary veterinarian regularly;
  • Follow all of the veterinarian’s instructions;
  • Give all medications according to instructions; and
  • Immediately inform the veterinarian of any significant change in the pet’s condition, such as increased difficulty breathing.

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 NC State 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.