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Your pet’s heart rate seems like such an elementary thing; but it gives veterinarians like me a great deal of information when it comes to understanding your pet’s health.
You can hear or feel much of what your veterinarian hears through his stethoscope when you borrow one, simply put your ear against your pet’s chest or feel the pulse in its groin. Without a stethoscope, you won't hear typical heart murmurs, but the pet's heart rate or rhythm provides considerable information as well.
Your pet’s heartbeat and pulse should be strong and regular. It is normal for the rhythm to change a bit in time with the pets breathing (sinus arrhythmia). Heart rate and respiratory rate often go up or down together since both are often adjusting to the dog or cat's current oxygen needs.
Large dogs usually have somewhat slower heart rate than small dogs and cats, while puppies and kittens have a slightly faster pulse and heart rhythm. Erratic (arrhythmic) pulses and abnormally slow pulses (bradycardia) or weak pulses often exist together and share many common causes.
Nervousness, fear or excitement are the most common causes of a fast heart rate. That is especially true when your pet confronts stressful situations - like a trip to the vet's office.
Exertion, pain, increased body temperature (such as heat stroke or fever), anemia, dehydration, shock (low blood pressure), congestive heart failure, cardiomyopathy, hyperthyroidism in cats, lung disease (eg pulmonary edema), air (pneumothorax) or abnormal fluids in chest (hydrothorax) can all result in a faster heart beat.
Heartworm disease in dogs, advanced age, tracheal collapse, diaphragmatic hernias, or cardiac tamponade can have the same effect.
Pets in late pregnancy (particularly with large litters) or overdose of medications (thyroid meds, catecholamines, amphetamine, caffeine, Sudafed, theophylline, atropine overdose, etc.) also can raise your pet's heart rate.
All medications that are considered stimulants (like like caffeine, chocolate or ADHA meds) can increase a pet's heart rate when consumed accidentally. Others, like phenylpropanolamine (Proin), are given to older female dogs to control bladder leakage (and occasionally to cats as well). Too high a dose of thyroid medications (levothyroxin) can also cause increased respiratory rate.
Heart disease in cats and dogs, trauma to the head (as in bell-ringer car accidents), increased pressure surrounding the brain can all affect the centers controlling heart rate.
All forms of circulatory collapse and shock, coma can slow heart rate as well.
Canine athletes have slower heart rates than couch potatoes.
Situations of low body temperature (hypothermia), low blood sugar (hypoglycemia), sedative medications or terminal FIP in cats all slow heart rate.
Elevated blood potassium levels (hyperkalemia), heart electrical circuitry failure (AV heart block, complete heart block), or hypothyroidism in dogs can cause a slower heart rate.
Overdose of many medications/sedatives (eg insulin, narcotics, general anesthetics, xylazine, digoxin, amlodipine and other calcium channel blockers, insecticides, propranolol and other beta-blockers, alcohol, neostigmine and other acetylcholinesterase inhibitors, etc.) will all slow your pet's heart rate.
Some rare diseases such as “sick sinus syndrome” (especially in old miniature schnauzers),
Benign sinus bradycardia (SB) occasionally occurs in dogs with no apparent bad health effects. It appears to be due to a sinoatreal node abnormality. SB occasionally occurs in immature or young dogs, especially cockers, dachshunds, pugs, westies and miniature schnauzers.
Stress can be the cause. But when it is not, interruption in the electrical signals that trigger your pet's heart contraction (AV block, complete heart block, etc.) as well as all the causes listed in reasons for bradycardia can also cause erratic heart rate or pulse.
Electrolyte imbalances (hyperkalemia), inherited heart electrical conductivity (“wiring problems”), atrial enlargement due to cardiomyopathy or heart valve disease, heart inflammation (myocarditis) can also cause an erratic heart rate or pulse.
Non-heart disease such as cancer, gastric (stomach) torsion or dilation, severe sudden trauma such as being hit by a car, two dogs in a fight or a cat mauled by a dog can affect pulse rhythm and rate as well.