Heart Disease Diagnostic Findings

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Several abnormalities might be noted in an animal with a heart problem. Most of these are due to poor perfusion of the target organ or fluid buildup due to changes in preload and afterload.

Difficult breathing or coughing due to fluid buildup in the lungs or thoracic cavity. This can be picked with the stethoscope during auscultation (listening to) of the heart and lungs. The term we use for an increased in lung sounds due to pulmonary edema is called rales.

Pale or bluish mucous membranes (cyanosis or anemia). This is noted when we look at your pet’s gums. Capillary refill time (CRT) might be prolonged.

Distended abdomen (ascites) due to back pressure of blood not flowing from the back of the body into the right heart properly.

This Doberman with heart failure shows the typical appearance of a distended abdomen caused by ascites. There are other diseases that can cause this look, including Cushing’s disease.

Distended jugular veins due to back pressure of blood not flowing from the head to the right heart properly.

This short movie shows distended and pulsing jugular vein

Pulse deficit- a lack of synchrony between the beating heart and the pulse.

Dr. P is checking for a pulse deficit by listening to the heart with the stethoscope while simultaneously palpating the femoral pulse. The two should be exact. If the heart rate is faster than the femoral pulse there is a pulse deficit, indicating an arrhythmia.

An increased heart rate (tachycardia)

A heart murmur during auscultation with the stethoscope

Cool extremities to the touch

Reduced mental capacity

Diagnostic Tools

Blood Panel

Many pets with heart failure are senior pets, so it is common for us to run a routine blood panel. There are no specific blood panel tests that diagnose heart disease in dogs and cats, although we can see indirect evidence of heart problems and their consequences sometimes. Also, the blood panel lets us assess problems in important organs like the kidney and liver that can occur simultaneously with heart disease in senior pets. This becomes important when we use medication to treat heart disease.

Thyroid Test

Our lab routinely performs a thyroid test on the blood panel for senior pets since a low thyroid level can be a cause of heart disease. This disease is called hypothyroidism, and occurs in dogs. A high level of thyroid hormone, called hyperthyroidism, occurs in cats, and can also cause heart problems. all pets 8 years of age or older should be checked for this hormone imbalance on a yearly basis.


A very important tool in the diagnosis of heart disease is the stethoscope. This simple yet elegant instrument allows us to hear the valves of the heart as they open and close, and also to hear the rhythm of the heart as it contracts. The name stethoscope comes from the Greek word “to spy on the chest”. It was designed in 1816.

We work with a wide variety of species, so we use different stethoscopes depending on the size of the pet. Each stethoscope has 2 different sized diaphragms, allowing us to hear heart sounds of different frequencies.

Animals have a normal arrhythmia, called sinus arrhythmia. This arrhythmia is an alternation in the rhythmic beating of the heart that coincides with breathing. This can easily be heard with the stethoscope. It is perfectly normal, yet does not occur in humanoids.

The stethoscope really comes into play for an animal that has a heart murmur. A heart murmur is a turbulence of blood flow as it goes through the heart valves (mitral or tricuspid). In a perfectly normal heart the blood flows past the valves silently, and all we hear with the stethoscope is the rhythmic lub-dub of the heart valves as they open and shut. If a murmur is present there is a whooshing sound mixed in with the lub-dubs, almost like the sound of a washing machine. This murmur is caused by blood becoming turbulent as it passes through an abnormal heat valve, although other problems can cause a murmur, the most notable being anemia. As we stated earlier, young animals can have an innocent murmur that resolves on its own and does not cause any problems.

Heart murmurs are graded from 1 to 6. One is barely audible with the stethoscope, 6 is so loud that you can feel the murmur with your hand on the chest. In general, the louder the murmur the more significant the disease, although this does not apply in all cases. Mitral murmurs tend to be louder due to the large difference in pressure (pressure gradient) between the left atrium and left ventricle.

In addition to their loudness, murmur have other audible characteristics. The sound can increase or decrease in intensity, a term we call crescendo or decrescendo. Murmurs that do not change in intensity are called holo.

Electrocardiogram (EKG or ECG)

As you already learned cardiac muscle (myocardium) is unique in its rhythmic beating. This rhythm is analyzed with an electrocardiogram. What the ECG measures is the depolarization (losing their electrical charge) and repolarization of the heart muscle as the cells contract. We talked about the mechanism of this in the cardiac muscle section in regard to sodium, potassium, and calcium. The ECG line that is produced measures the direction of the electrical activity along with its magnitude. Since the atria are smaller in size than the ventricles, their magnitude on the ECG strip is smaller.

The hardest part about performing an ECG on an animal is keeping it still enough to get a good reading. Sedatives are not used since they can interfere with the results. Interpreting the ECG is a medical art, and requires the familiarity of the electrical differences of many different breeds of dogs and cats. We used a service that allows us to transmit the ECG through the telephone or via fax to a group of veterinary cardiologists that specialize in ECG’s. In addition to interpreting the ECG, they also give us a cardiac consultation via fax the next day (or within a few minutes if it is an emergency).

This is one of their reports from a dog with a normal ECG that happened to have diabetes

We use the ECG in several situations. The first is for a dog or cat that is older or might have the symptoms of heart disease, especially coughing. We also use it prior to any anesthesia in high risk pets or when there is significant concern about anesthesia in general . We have a complete page on anesthesia to learn more.

Here is the report on a Doberman with severe cardiomyopathy

An ECG alone cannot determine if heart failure is present. It can be helpful in determining that heart failure is not present.

This ECG is from a pet that stayed still long enough for us to get a reading. It shows almost 4 complete beats of the heart.

We enlarged one of the 4 beats to help when we explain below.


When the SA node fires it stimulates the cells of the atria to depolarize. The ECG picks this up as a small positive deflection on the strip

QRS Complex

As the electrical current flows into the ventricles during depolarization the ECG produces the 3 distinct wave patterns that make up this complex. There are 3 peaks because of the way the current spreads in the ventricles, going from inside to outside. These 3 peaks are larger than the P-Wave because the size of the ventricles are much larger than the atria.


When the ventricles repolarize they produce the T-Wave. Repolarization in general should produce a negative peak on the ECG strip, but because it is occurring in the opposite (outside to inside this time) direction as the depolarization of the ventricles, the peak is positive on the ECG strip.

Lets look at a few of the abnormalities the ECG is good at detecting….


An abnormally slow heart rate is called bradycardia. On the ECG strip this is noted as less P-waves, QRS complexes, and T-Waves per minute. For the average dog, this means a heart rate (HR) less than 60 beats per minute, and for the average cat, less than 80 beats per minute. This varies with breed and size. A severe bradycardia can cause a dog or cat to become weak, have a low blood pressure, and literally pass out (syncope). It passes out because of inadequate perfusion to the brain cells.

Listed below are some causes of bradycardia:

Respiratory disease

Gastric ulcer


Hypothermia (low body temperature)

Hypoglycemia (low blood sugar)


Hyperkalemia (high potassium)

Heart Blocks

These are a group of disorders that occur when the electrical current that flows from the atria to the ventricles is disrupted. They are identified as 1st, 2nd, and 3rd degree.

1st Degree Heart Block

This is a minor problem that is detected on the ECG strip as a prolonged time between the P-Wave and the R-Wave. This means there is a prolonged conduction across the AV node. It might be normal, from digitalis therapy, or due to hyperkalemia. Treatment is not required usually.

2nd Degree Heart Block

This slightly more important problem is detected on the ECG strip as a P-Wave without a corresponding QRS complex following it. It arises when there is a failure of the SA node to activate the ventricles after it has activated the atria. This means there is a failure of the SA node to stimulate the AV node. It could be normal on some dogs, caused by respiratory disease, or even caused by digitalis again. Most dogs are not treated, although atropine can be used.

There is a version of the 2nd Degree Heart Block called the Mobitz Type II that has the potential to be more severe. In this case the current does not pass through the bundle of His or bundle branches. If the heart rate becomes slow enough it can reduce cardiac output. It can be caused by scar tissue in the heart muscle, death of heart muscle cells, infection, and cancer. It can lead to a 3rd Degree Heart Block, so when it occurs, it needs to be monitored.

3rd Degree Heart Block

In this serious arrhythmia there is no coordination between the atria and ventricles. There will be P waves and QRS complexes, but they will not be in their usual coordination of a P Wave before every QRS and a QRS after every P Wave. The cause might be congenital, low oxygen, inadequate blood supply to the heart cells, inflammation, trauma, hyperkalemia (high potassium), cardiomyopathy, surgical trauma, and digitalis.


This is an abnormally fast heart rate. For the dog this means over 160 beats per minute, for the cat, over 200 beats per minute. This varies with breed and size. It is detected on the ECG as a high number of P-Waves, QRS complexes, and T-Waves per minute.

It can be caused by heart failure, pain, fever, hyperthyroidism in cats, anemia, and of course, excitement. When the underlying cause is treated the problem tends to go away.


An excellent tool in the diagnosis of heart disease is radiography. The size of the heart and pulmonary vessels, along with fluid buildup in the lungs, can be seen in a radiograph. We will show you some normal radiographs first, then some abnormal ones. You might one to come back to the normal ones to refresh your anatomy as you view the abnormal ones.

Before we get to the radiographs lets review some thorax anatomy


You might want to do a more detailed review at our heart anatomy page

We will also show you radiographs of pets with breathing problems that are not the result of heart disease. This shows the importance of radiography in diagnosis, and emphasizes the need to follow the diagnostic process at all times. Don’t forget that changes in the lungs can eventually cause the right heart to fail (cor pulmonale).

Normal dog heart and lungs side view (called a lateral view). The head is towards the left. The trachea is in the correct location and is of the proper size. The dark lungs are readily visible along with the normal sized heart. PVC is posterior vena cava.



Normal dog heart and lungs top view (called a DV (Dorsal-Ventral) view). The heart is the correct size, and it is surrounded by normal lung tissue. The lung tissue is black because it is filled with air. The white semicircular area at the bottom is the diaphragm.



There is significantly more information in a chest radiograph than just the trachea, heart and lungs. In this radiograph you can see the aorta along with an artery (A), bronchus (B), and vein (V) to the cranial lung lobe. Changes in the size of these veins and arteries give us clues as to whether heart disease is present along with the cause of the heart disease.



An even close view of the artery (A), bronchus (B), and vein (V)


Normal cat heart and lungs side view. You can see the same structures as the dog radiograph. Do you see the artery, bronchus, and vein to the cranial lung lobe? They are smaller than the dog, but they are present. Do you also see the posterior vena cava? The arrow points to it.



A cat from the top view (DV). Its not easy to get a cat to sit still to take this radiograph!



We work on all different kinds of critters that get heart disease. This is a ferret


This is a guinea pig


An enlarged heart is called cardiomegaly. There are several parameters we use to give us an indication a heart is enlarged. These parameters are variable, and depend heavily on the breed of dog. We will show you a dog with heart disease. We put a normal heart radiograph after the diseased one for comparison.  A labeled radiograph is also below.

This dog has a very large heart (cardiomegaly). Not all pets with heart disease show such obvious and extreme changes. Many changes are subtle, and do not show up well on a web site at low resolution, so an extreme one is used for better understanding. We would hope to see a dog like this long before the radiograph progressed to this point.


The radiographic diagnosis is elevated trachea, mainstem bronchus compression, loss of caudal waste, loss of cranial waste, pulmonary edema, and increased sternal contact. The diagram below illustrates the  structures.


Normal dog again for comparison


Cardiomegaly on a Dorsal Ventral (DV) view


Normal dog again for comparison


Not every enlarged heart (cardiomegaly) is a sign of heart disease. This cat has an apparently enlarged heart with an elevated trachea. In this case it is caused by a diaphragmatic hernia, where the liver has literally torn through the diaphragm and resides in the thorax.


Sometimes the hernia is not so apparent, and makes it look just like an enlarged heart.


Radiographs are also used to diagnose pulmonary edema, which is fluid buildup within the lungs themselves. It is a sign of congestive heart failure. All the whitish area at the the top right of the lungs is the fluid. Normally this area should be black because it is filled with air.

This is a a large amount of pulmonary edema in a different case.



When the  left atrium is enlarged it is also a sign of heart failure. We can see an enlarged left atrium radiographically if it is large enough.

The arrows point to a very enlarged left atrium at the arrows


The previous radiograph changes were due to failure of the left side of the heart (left atrium and left ventricle). If the right side of the heart goes into failure, the radiograph might show fluid in the abdomen and no changes in the thorax.

This cat has ascites, which is fluid buildup in the abdomen. If you compare it to the radiograph below it you can see that individual internal organs are not visualized. This is because the organs are surrounded by fluid. The dark areas are air in the stomach and in the intestines. Heart disease is not the only problem that can cause ascites. Several other conditions can give this radiographic appearance, especially FIP in cats and cancer.


This normal cat abdominal radiograph shows all the distinct internal organs for comparison to how the fluid above obscures them


Time for a break from all this radiology stuff. Lets look at something fun. It is the beating of the heart of a tortoise that is undergoing bladder stone surgery. Click on the video and enjoy the beat.


An echocardiogram of the heart is almost indispensable in detecting a significant number of heart problems. Echocardiography refers to the imaging of the heart with ultrasound. Echocardiography may be divided into three types based on the instrumentation and application. These are M-mode, Two-dimensional, and Doppler Echocardiography.


This image is useful to measure the thickness of the ventricular walls along with size of the cardiac chambers. With these measurements a formula is used to determine cardiac contractility.


Two Dimensional

This image gives us an overall view of the heart. We can look into the chambers and see the valves in action. We can also see fluid around the heart if it is present.

This ultrasound picture shows the left ventricle (LV), aorta (AO) and left atrium (LA)


Here is the report on just some of the measurements obtained and calculated during an ultrasound



The Doppler view allows visualization of the blood as it literally flows through the heart. It is usually performed simultaneously with the Two Dimensional image. It can sometimes help us detect the degree of valvular disease by measuring the speed at which the blood flows through the abnormal valve.

In the top half of this ultrasound picture the 2 parallel running vertical lines are the doppler measuring the blood flow through the mitral valve. The “MR” at the bottom half of the picture is the doppler measuring the intensity of the mitral regurgitation that is occurring.


The color doppler makes it easy to visualize the blood flow through the heart valves


Double click on the movie below to watch the color doppler in action.  Notice how fast this heart is beating. Remember our earlier lesson on heart failure, and one of the ways the body adapts to a heart that is not pumping enough blood is to increase the heart rate. That is occurring in this case.

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Cardiac Diseases and Treatments

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Heart Disease Overview Page

Vascular Anatomy & Physiology>

Heart Anatomy & Physiology

Causes and Symptoms of Heart Disease

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