Heart Disease Pathology

There are many things that contribute to the development of heart disease and heart failure. Genetics can play a huge role in predisposing ferrets to heart disease. Other factors that can contribute to the development of heart disease in any animal include viral or bacterial infections, parasites, cancers, and other systemic diseases that may put strain on the heart, as well as various medications. In addition to many different causes, there are many different types of heart disease. While some heart disease is congenital (a developmental defect present at birth), most cases develop later in life, when the ferret is an adult (referred to as acquired heart disease). It is important to be aware that while more common in older ages, heart disease can develop at any age. Below we will review simplified descriptions of some of the basic types of heart disease in ferrets that may lead to the development of heart failure.

For more practical information on how to recognize symptoms of heart disease and some of the treatments that can be prescribed by your veterinarian, check out our page on Heart Disease Overview. To read about how symptoms can develop, see Heart Disease – Symptoms. For more in-depth information on diagnosis, see Heart Disease -Diagnosis. For more in-depth information on treatments, see Heart Medications.

Heart Function

Before diving into a discussion on the ways that a heart can be diseased, you may want to understand the basics of how a healthy heart works. The heart is responsible for pumping oxygen and nutrient rich blood to all of the important tissues and organs in the body. A very simplified way to think of the heart is as a muscular sack. This muscular sack squeezes to pump blood through the body, and then relaxes to fill with more blood.

Oxygenated blood (red) flows from the lungs through the pulmonary veins, into the heart. The heart then pumps the oxygenated blood into arteries, which course through the entire body. The tissues and organs of the body take the oxygen and nutrients from the blood, and deposit waste and CO2 into the blood. This deoxygenated blood (blue) travels from the body to the heart via veins. The heart then pumps this blood, via the pulmonary arteries, into the lungs, where CO2 is released and O2 picked up. The freshly oxygenated blood then returns to the heart and the cycle is repeated.

Special valves in the heart prevent the blood from flowing backwards. When certain parts of the heart squeeze, these valves open to allow blood flow. When they relax, the valves close to prevent any back-flow of blood.

The heart’s rhythm is orchestrated by a complex electrical conductive system. You can imagine this as an electrical circuit controlled by a natural pace-maker. The conductive system works to make sure the correct parts of the heart squeeze and relax at the correct times, so the heart pumps with a strong and regular beat. A normal ferret heart rate is from 160-250 bpm.

Now that you know the basic components of a functioning heart, let’s discuss how the heart can malfunction.

Types of Heart Disease

There are several different types of heart disease. Three categories will be discussed below. However, note that there are other types of heart disease not covered in this article including infectious and inflammatory diseases.

Electrical

Electrical dysfunction of the heart occurs when the conductive system (the “electrical circuit”) of the heart is not working properly. This can result in the heart beating irregularly, too quickly, too slowly, or a combination of the above. These abnormal rhythms are called arrhythmias. There are many different types of arrhythmias, and proper diagnosis requires an Electrocardiogram (often called an ECG or EKG). Unfortunately many owners are unwilling or unable to obtain an EKG for their ferrets; as a result we have less information that is readily available on ferret arrhythmias.

Some arrhythmias can be treated with medications, but many require surgical treatments, such as a pacemaker, that are not yet widely available for ferrets. Check out our Hall of Fame to read about one ferret who did get a pacemaker.

Some arrhythmias can result in sudden death. Often, arrhythmias cause significant strain on the heart muscle which over time can result in cardiomyopathy, and eventual heart failure.

Valvular (Structural Disease)

Another type of heart disease occurs when the heart valves do not function properly. The valves of the heart are one-way valves which open when the heart squeezes, and close when it relaxes. Valvular heart disease can result in the valves either not opening, or not closing properly. Valvular disease is diagnosed with an Echocardiogram (often called an Echo).

Valvular Stenosis:

Stenosis is when a valve does not open properly. The word stenosis means a narrowing – in other words, the valve opening becomes narrowed, which reduces the amount of blood that can flow through. Imagine trying to squeeze mustard out of a bottle that has a clogged opening. You must squeeze extra hard to get the mustard to come out and when it does, it is a small stream. In the same way, if a valve does not open properly, the heart must squeeze extra hard to pump the blood through. Over time this causes significant strain on the heart and can ultimately lead to cardiomyopathy and eventual heart failure.

Valvular Regurgitation:

Regurgitation occurs when a valve does not close properly. When this happens the heart pumps blood out normally, but when it relaxes to fill up with new blood some of the blood it pumped out flows backwards back into the heart. This means that the heart now fills with more blood than it should, and can even cause the incoming circulation to get “backed up,  or congested. This can force the heart to work harder, and can eventually stretch out the heart muscle, leading to cardiomyopathy and in time, heart failure.

Muscular – Cardiomyopathy (Structural Disease)

When heart disease occurs in the heart muscle, this is called cardiomyopathy (abbreviated CMY). “Cardio” means heart, and “myopathy” means disease of the muscle; thus “cardiomyopathy” – heart muscle disease. Over time electrical and valvular diseases of the heart can both progress to the development of cardiomyopathy. Cardiomyopathy may also happen as an isolated problem. There are 2 primary types of cardiomyopathy in ferrets – Hypertrophic and Dilated. Both of these will eventually be visible on X-Ray as an enlarged heart; an Echo can provide more accurate information on which type of heart disease is present. In time, most cases of cardiomyopathy eventually progress to Heart Failure.

Hypertrophic CMY:

Hypertrophic Cardiomyopathy is thought to be somewhat rare in ferrets, but it is unclear if this is because it truly happens less, or we simply notice it less. Hypertrophic CMY occurs when the muscle of the heart becomes thickened and stiff. The heart is a muscle; similarly to how you can lift weights at the gym to build up bigger biceps, a heart that is forced to work under great strain can become enlarged and thickened.

A normal heart muscle is stretchy (like an elastic sack or balloon), allowing it to expand and fill with blood when relaxed. When the heart muscle becomes thickened, the walls become stiff and it is unable to effectively stretch to fill with blood. This causes the circulation to build back-pressure that the heart then has to pump harder against. Over time this strain can lead to heart failure. Unfortunately, many ferrets who do have Hypertrophic CMY suffer from sudden death.

Dilated CMY:

Dilated Cardiomyopathy is by far the most form of heart disease in ferrets and is seen in up to 80% of ferrets with heart disease (2). In this case, the heart becomes enlarged and stretched out. As the muscles stretch and thin, the strong muscular pump of the heart begins to resemble something more like a round, floppy sack. The muscle cannot pump as hard so, while the heart holds more blood, it is too thin and weak to effectively push the blood through the body. When Dilated CMY becomes advanced enough, the heart is so stretched that it loses its shape and appears round in shape – called a “globoid” heart.

Below is a picture of Koda as a kit, showing a normal, healthy ferret heart. Note the small size, and oblong shape. (Note also his intestinal Blockage – naughty ferret).

The next photo (same ferret) taken at just over 7 years old demonstrates a globoid heart due to advanced cardiomyopathy. Note the very round appearance of the heart – like a globe. Also note the increased size within the thorax, and how the heart touches the diaphragm.

Heart Failure

Heart Failure (HF), often called Congestive Heart Failure, or CHF, occurs when the heart is so diseased that it can no longer pump blood effectively enough to meet the body’s demands. This results in several symptoms, a few of which will be discussed below.

Diagnosis: 

To read more see Heart Disease – Diagnosis.

Heart Failure is best diagnosed via Echo, which will tell you how poorly the heart is functioning, and can also reveal what the underlying cause(s) of the failure may be, and which specific parts of the heart are failing. However, a simple X-Ray demonstrating an enlarged heart, combined with classic symptoms of heart failure, are often sufficient to make a presumptive diagnosis of heart failure. X-Rays are quick, easy, and inexpensive and can be invaluable for catching heart disease early and helping to diagnose heart failure, among other diseases.

Note that an enlarged heart on X-Ray without significant symptoms may be indicative of Cardiomyopathy (Heart Disease) that has not yet progressed to Failure. Symptoms of HF without an enlarged heart on X-Ray warrants further investigation which may include an Echo, EKG, and blood work.

A note on murmurs: While a heart murmur in a ferret is almost always abnormal, a heart murmur alone is NOT sufficient to diagnose Heart Failure. Additionally, the severity of a murmur does NOT always correlate with the severity of the heart disease. If your vet detects a murmur on exam, or any other abnormal heart sounds, you should request that they follow through with further workup. Additionally, not all ferrets with heart disease will have an audible murmur. If you suspect your ferret has heart disease, you need to request your vet does further workup.

Sources:

1. Johnson-Delaney, C. (2017). Ferret Medicine and Surgery. Boca Raton, Fl: Taylor & Francis Group, LLC.
2. Lewington, J. (2007). Ferret Husbandry, Medicine, and Surgery, 2e. Philadelphia, PA: Elsevier.
3. Quesenberry, K., Carpenter, J. (2012).  Ferrets, Rabbits and Rodents Clinical Medicine and Surgery, 3e. St. Louis, MO: Elsevier.