Heart Murmurs in Pets

I am addressing a topic submitted to me by a friend, Megan, who I hope finds this helpful! Megan's question:  "What exactly does a heart murmur mean for your pet? What causes it, is there anything to be done to lessen the effects on the heart, and how does it change their health outlook?"
A heart murmur is a condition of the heart where a valve is not closed all the way and so the normal flow of blood in the heart itself is disrupted. There is a back flow of blood that happens and makes a "whoosh whoosh" sound when the veterinarian or veterinary technician listens to your pet's heart. Heart murmurs are graded on a scale of I to V (1 to 5), with Grade V being the worst.
This valve issue can be caused by a number of things. Number one is genetics. Some pets are born with the valves not developed correctly. Puppies can however have a murmur that will go away on its own as the heart grows and matures. This is usually not an issue and will resolve itself. When it does not go away as your pet ages, you may need medications to help your pet during its life, which I will discuss later. Number two is heartworm disease. Dogs and cats can, and do, get heartworms. When a mosquito bites your pet, it puts the babies (called larvae) in their system. Those travel in the blood stream, go to the heart, and live as adult heartworms in the valves. This is a very serious disease that causes murmurs and death. Keeping your dog and cat on heartworm prevention (even if it's indoors-mosquitoes come in the house!) and having it tested every year is the best way to ensure your pet does not pick up these nasty pests. Number three is old age. As your pet becomes a senior citizen, the valves of the heart will weaken and a murmur will develop. This is a fairly common occurence with older pets.
As far as your pet's health outlook, you may notice your pet is a little more tired or gets out of breath more easily. Exercise may be difficult. Some pets will develop a cough as the back flow of blood can cause fluid to accumulate elsewhere in the body. Sometimes, there may be no outward signs or symptoms at all.
If your pet has a murmur, there is not really anything that can be done to lessen the effects on the heart itself but you can help ease your pet's symptoms. Your veterinarian can prescribe a drug called Furosemide (or a similar medication) to help decrease fluid build up in the body. Your pet may need to pee more often while on this medication. Some other drugs that may be prescribed are Enalapril or Vetmedin. Both of these meds help blood flow more smoothly so the heart can pump blood more efficiently with less work. It is also a very good idea to have bloodwork done by your veterinarian yearly to make sure your pet's other organs, electrolytes, and blood counts are staying in healthy ranges. By doing a combination of the bloodwork, medication, heartworm prevention, and visiting your veterinarian regularly, a pet with a heart murmur can still live a normal life for years to come.