By Dr. Laura Hady
While February is heart awareness month for humans, I believe we need to raise heart disease awareness for pets and their owners this month. According to The Drake Center, about 10 percent of all dogs seen in family veterinary clinics have heart disease, but I have experienced a much higher percentage (greater than 50 percent) as dogs get older. Fewer cats are diagnosed with heart disease, mainly because they do not exhibit symptoms like dogs do, such as cough, exercise intolerance and pale gums.
The following are some basic facts about how the heart and the circulatory system works in different animals:
- The human heart beats an average of 115, 000 times a day; the whale has a slower number of heart beats per day and hummingbirds have a much faster heart rate. The heart can continue beating even when it is disconnected from the body. Human pace makers can be donated after death, then they can be cleaned and reset to function in a dog.
- The cardiac conduction system is an electrical conduction system of the heart. If the heart has too many irregular beats, then weakness or collapse can occur. Some animals have what is called a sinus arrhythmia, meaning that their heart briefly stops when they breathe.
- A human heart pumps about 2,000 gallons of blood a day. The amount may be slightly less or more in animals depending upon the size of the animal. The heart returns low oxygen blood to the heart via veins and then pumps out oxygenated blood to the tissues via the arteries.
- The most common cause of heart disease in dogs is mitral valve dysplasia or regurgitation – where the valves on the left side become floppy and there is a mix of oxygenated and unoxygenated blood – so the heart is not as effective as a pump.
- Hearts have different structures in different animal species. The pig’s heart is closest in size and function to humans. Pig hearts are used in both full heart transplants and also to replace valves that are not working properly. The biggest heart is in the blue whale, and the smallest heart is in the fairy fly-wasp. In the giraffe, part of the left side of the heart is bigger, which is the opposite in humans, dogs, and cats. The reason for this change in size is because the blood must get pumped efficiently up a giraffe’s long neck to bring oxygenated blood to the brain. The heart in a zebra fish has regenerative properties to mend injuries, and this is a focus of new research for human hearts.
- The beating of the dog and cat heart is caused by the valves of the heart opening and closing. Abnormal sounds in blood flow through the heart are called murmurs.
- Normal heart function is maintained by a regular heart beat with a controlled rate and rhythm by the electrical conduction system. Problems with this system can cause an uncoordinated rhythm called an arrhythmia.
Stay tuned for Part 2 next month, where we will discuss the different types of heart diseases most commonly found in dogs and cats.