Most pet parents don’t think about the heart until a veterinarian mentions hearing a murmur during a routine visit. That moment can feel confusing and often concerning.

Heart conditions in dogs and cats often develop quietly, without obvious signs at first. Becoming familiar with basic heart anatomy and terms like murmur, arrhythmia, and heart failure, along with common heart medications, can help you feel more informed and less anxious if the topic ever comes up during an exam.

Let’s Dive into the Basics: Plumbing and Electricity

Plumbing

Think of the heart as a house. It has “plumbing” (four valves, four chambers, and various vessels directing blood from and to the body) and “electricity” (special cells that initiate contraction and relaxation of the heart muscles). While the heart itself has no “HVAC system”, it most certainly interacts closely with the lungs to help pump oxygen-rich blood to the body, and bring back CO2-rich blood from the body.

Looking at Image 1 below, you can use your finger to trace the flow of blood.          

1. Blood returns from the body through two large veins called the venae cavae.
2. It enters the right side of the heart, which acts as a pump. 
3. It then flows through the right atrium and ventricle chambers and one-way valves (the tricuspid and pulmonic valves). These valves are “one-way doors” that keep blood moving in the correct direction.
4. Blood is then pumped into the lungs to offload CO2 and pick up oxygen. 
5. Oxygen-rich blood returns to the left side of the heart. 
6. It then flows through the left atrium and ventricle and through two more one-way valves (the mitral and aortic valves).
7. The oxygen-rich blood is then pumped to the rest of the body through the aorta.
   

Image Source: Human Kinetics

This is the “plumbing portion” of the heart! When there is an abnormality with the plumbing of the heart we say the heart has a mechanical dysfunction, and you should automatically think about a dysfunction with one of the valves or chambers in the heart.

Electricity

Now, let’s briefly talk about the electrical portion of the heart. We mentioned that we have plumbing (i.e. four valves, four chambers, and various vessels), but we need a driving force to push the blood through them all. This is where the electrical portion of the heart comes into play. Without getting too technical, realize there are certain specialized cells inside the heart muscle that, when activated, help the heart muscle contract and push the blood through our four-legged loved ones’ bodies. This amazing electrical activity can be recorded in real time using something called an ECG, or electrocardiogram. 

In Image 2, you can trace the electrical activity as it happens in the heart, and how it reflects on the ECG. The heart diagram on the left corresponds to what happens on the ECG on the right. 

1. The electrical activity starts with the SA node, which helps contract the top chambers of the heart (the atria). 
2. It then goes to the AV Node and continues to the bottom of the heart, to help contract the bottom chambers (the ventricles). 
3. Once a muscle contracts (depolarizes, in yellow below), it then must relax (repolarize, in red below). Contraction/depolarization results in pushing blood through the heart’s chambers. Relaxation/repolarization results in filling of blood inside the chambers. 
4. And the cycle continues on and on.
   

Image Source: BRI ED Teaching

This is the electrical portion of the heart! When there is a problem with the electrical system of the heart, we call it an arrhythmia; this is an electrical dysfunction. There are various types of arrhythmias. 

Dysfunctional electricity results in premature or delayed contraction of the associated chamber, creating volume-delivery abnormalities. The heart has a very specific way it contracts and relaxes, and it’s very important to keep it pumping appropriately.

Heart Tests, Common Conditions, and Signs to Watch For

Common Heart Tests

To assess the structures of the heart, we often recommend chest X-rays and an Echocardiogram. X-rays (also known as Radiographs) allow for assessment of the heart size and shape, and signs of congestive heart failure (such as fluid in the chest cavity). An Echocardiogram is an ultrasound of the heart. It allows for evaluation of chamber size, wall thickness, how well it pumps, valve function and appearance, and pressure activity  across the heart. As mentioned above, an ECG is the test used to assess arrhythmias, as it shows us the electrical conduction during each heartbeat. 

Finally, we use a test called ProBNP to assess the health of the heart muscle, especially in cats. ProBNP is a cardiac biomarker released when the heart muscle is stretched. We use it to help detect and assess heart disease in our furry loved ones.

Most Common Diseases in Dogs and Cats

In Dogs:

• Valve Disease (most commonly the Mitral Valve) – This is a disease in which the valve becomes thickened, stretched, and floppy, so it can’t close tightly anymore. It’s most commonly linked to genetics and aging, especially in small-breed dogs like Cavaliers, Dachshunds, and Chihuahuas. Over time, this makes the heart work harder and can lead to coughing, tiredness, or trouble breathing.
• Dilated Cardiomyopathy (DCM) – This is a disease in which the heart muscle becomes weak and stretched, causing the chambers to enlarge and the heart to pump blood poorly.

In Cats:

• Hypertrophic Cardiomyopathy (HCM) -This is a disease in which the heart muscle becomes abnormally thick, making it harder for the heart to relax and fill properly.
• Restrictive Cardiomyopathy (RCM) – is a disease in which the heart muscle becomes stiff and less flexible, impairing normal filling despite normal or near-normal wall thickness. 

Both dogs and cats can also experience rhythm problems and heart defects from a very young age. Heart disease often leads to a condition called Remodeling. A remodeled heart is one that has undergone changes in heart size, shape, and function. Heart remodeling often results in scar formation due to changes on a cellular level. What starts as a defense mechanism soon results in reduced function. 

Image Source: UC Health

Signs Pet Owners Should Watch For

• Early signs may include coughing in dogs, tiring easily, fainting, lethargy, or faster breathing while resting or sleeping.
• More serious warning signs include labored breathing, blue gums, collapse, restlessness, or a racing heartbeat, which require immediate veterinary attention.
• During an exam, we listen carefully to the heart and lungs, check pulses and gum color, and may recommend the tests mentioned above to understand what is happening.
• At home, monitoring your pet’s breathing rate while sleeping, watching for changes in energy or appetite, and keeping track of daily patterns can be helpful to share with your veterinarian during visits.  

Helpful Tip: A really easy test you can perform is called the Resting Respiratory Rate. This is done by counting the number of breaths per minute when your pet is fast asleep. If the number is above 30, we recommend you bring your little one in for an evaluation, as they may have fluid build up in their lungs, secondary to heart disease.   

Common Treatments for Heart Disease

Even though valve disease is the most-common disease in dogs, valve replacement surgery is not common practice as of this publication. However, some universities are actively pursuing this treatment model, and we expect this to eventually become more common. Today, treatment for heart disease is focused on reducing clinical signs and slowing down disease progression.  

Treatments for heart conditions truly depend on the specific disease at hand. When there is evidence of mechanical dysfunction, such as chamber abnormalities, we often include medications that reduce fluid buildup, ease the heart’s workload, and support its function.  

Commonly Used Medications 

• Pimobendan – Used to increase the heart’s ability to contract and dilate the veins across the body. Vein dilation reduces the pressure the heart has to push against when pumping blood.
• Furosemide (commonly known as Lasix) – A diuretic used to remove excess fluid in congestive heart failure. Reducing fluid results in less volume the heart has to handle when pumping blood. 
• Spironolactone – Helps reduce fluid retention, the volume of fluid the heart has to handle, and reduces heart muscle remodeling. 
• Enalapril and Benazepril (ACE Inhibitors) – These are medications that help relax blood vessels and lower blood pressure, making it easier for the heart to pump blood. They reduce the strain on the heart over time. 
• Clopidogrel – This is a medication used to prevent blood clots, commonly used in cats with HCM.

For electrical dysfunctions, such as heart arrhythmias, we often recommend medications that control the heart rate. Commonly used medications include Atenolol, Sotalol, Diltiazem, and Digoxin.

The Role of Nutrition 

We also often recommend dietary adjustments such as a reduction in salt intake and an increase in omega-3 fatty acids intake.  Reducing salt intake helps reduce fluid retention, which makes the heart’s job easier. Omega-3 fatty acids are natural anti-inflammatories and act as a cardiac muscle protectant. An excellent source of Omega-3 fatty acids is fish oil.

Final Thoughts

Heart disease is not limited to senior pets. It can affect pets of any age, and early detection plays an important role in maintaining health, comfort, and quality of life. If you notice changes in breathing, behavior, or energy levels, it is important to speak with your veterinarian.

At Wags, we have advanced tools and technologies. With sophisticated diagnostics, an in-house lab and digital X-rays, our experienced clinicians can have the answers you need in minutes.

During your visit, we spend all the time you need so you can feel informed, empowered and confident in the care your pets receive. With simple monitoring at home and regular veterinary visits, many pets with heart conditions continue to live happy, active lives for years. Get in touch with us. We’re here to help!

• March 2, 2026
• CPR ADMIN