Episode 16  ·  12m 15s

Congestive Heart Failure — Why It Looks So Different in Dogs and Cats

Dr. Michael LoSasso, DVM & Julie Schwenzer Frisco Emergency Pet Care
Heart disease Cavalier King Charles Heart murmurs Cats Ultrasound diagnosis Oxygen therapy
"Heart disease in pets can be subtle until suddenly it isn't. Today we're breaking down what congestive heart failure really looks like, how it develops, and the early signs pet parents should never ignore."
— Julie Schwenzer

Episode summary

Congestive heart failure is one of the more common — and more misunderstood — diagnoses Dr. LoSasso sees in his emergency hospital. In this episode, he breaks down what's actually happening inside a failing heart, why it hits small dogs the hardest, and why the same disease is almost invisible in cats until it's a crisis.

The mechanics start with a valve problem. The heart's valves are supposed to keep blood moving in one direction only; in dogs with congestive heart failure, a valve doesn't seal properly and blood leaks backward. That backward flow is what produces a murmur — but a murmur by itself isn't disease. Many dogs live with a murmur for years, sometimes their whole life, without ever developing true heart failure. It's only once the backward flow becomes severe enough that blood pressure in the lungs' vessels forces fluid to leak into lung tissue — and that's when breathing gets hard and the coughing starts.

"A murmur is not disease. It just says there's inappropriate blood flow. Dogs in congestive heart failure almost always have a significant murmur — but you can have a significant murmur and not have heart disease. You have to look farther, either with X-rays or ultrasound."
— Dr. Michael LoSasso, DVM

It's overwhelmingly a small-dog disease — Dr. LoSasso says his congestive heart failure patients are typically 20 pounds or less, with Chihuahuas, Schnauzers, and Dachshunds showing up often. The breed most associated with it is the Cavalier King Charles Spaniel, which he calls "the poster child" for the condition — frequently developing heart failure by age seven or eight, essentially carrying an old dog's heart at a middle-aged dog's age.

For diagnosis, he favors ultrasound over X-ray when the dog will tolerate it — it can directly show fluid in the lungs, tends to cost less, and doesn't require the dog to lie on its back. Acute treatment is an oxygen cage (roughly doubling available oxygen) combined with furosemide (Lasix) to pull fluid out of the lungs; dogs typically go home on oral furosemide plus heart medications. He notes that starting pimobendan early in a dog that already has a murmur has been shown in studies to delay, and sometimes prevent, the onset of full congestion.

Cats hide this disease almost completely

Cats commonly develop a different condition — hypertrophic cardiomyopathy — and rarely cough the way dogs do. Warning signs are late and subtle: reduced activity, open-mouth breathing, a high respiratory rate. Some cats have no murmur and no prior signs at all, and are only discovered when they're in acute distress from a clot, or found deceased. Dr. LoSasso calls heart disease in cats "a silent killer." Treatment can include Lasix, oxygen, pimobendan, and Plavix to reduce clot risk — but twice-daily oral medication is a real logistical challenge for most cat owners.

Questions answered in this episode

The following questions are answered by Dr. LoSasso in this episode, drawn directly from the conversation. These are real clinical answers from a practicing emergency veterinarian with 30+ years of experience.

Dr. LoSasso explains it's fluid buildup in the lungs caused by valvular dysfunction. The heart's valves are supposed to keep blood flowing in one direction, but when a valve doesn't seal properly, blood leaks backward into the lungs. Under pressure, that blood starts to leak fluid into lung tissue, which impairs the pet's ability to exchange oxygen for carbon dioxide — and frequently causes coughing in dogs.
No. Dr. LoSasso is clear that a murmur is not disease — it's just the sound blood makes moving abnormally through a valve. Many dogs live with murmurs for years before, if ever, developing actual congestive heart failure. Dogs in heart failure almost always have a significant murmur, but a dog can have a significant murmur and never develop heart disease, so the murmur alone can't tell you whether congestion is present.
Dr. LoSasso says it's typically smaller dogs, usually 20 pounds or less — Chihuahuas, Schnauzers, and Dachshunds are common, but Cavalier King Charles Spaniels are the classic example. He calls them the poster child for the condition, since they're well known for developing left-sided heart disease often by seven or eight years old.
Dr. LoSasso says a persistent cough in an older small-breed dog should be checked with X-rays or ultrasound. He personally favors ultrasound — it can directly show fluid in the lungs, is often less expensive, and is less stressful for the dog than X-rays, since it doesn't require lying on its back. He notes a murmur alone can't confirm congestion; imaging is needed to actually see fluid in the lungs.
Dr. LoSasso describes acute treatment as an oxygen cage, which roughly doubles the oxygen available to the pet, combined with furosemide (Lasix) to pull fluid out of the lungs. Once stabilized, dogs typically go home on oral furosemide plus heart medications. He notes that pimobendan, started early in dogs with a murmur, has been shown in studies to delay or in some cases prevent the onset of congestion.
Dr. LoSasso explains cats commonly develop hypertrophic cardiomyopathy and, unlike dogs, usually don't cough. Warning signs are subtle and late-stage: reduced activity, open-mouth breathing, and a high respiratory rate. Some cats have no murmur or any prior indication of a problem and are simply found in distress from a clot, or found dead, from a condition they were born with. He calls it a silent killer in cats.
JulieHeart disease in pets can be subtle until suddenly it isn't. Today we're breaking down what congestive heart failure really looks like, how it develops, and the early signs pet parents should never ignore. Doctor, could you please break down what congestive heart failure is, particularly in dogs and cats?
Dr. LoSassoGood morning, Julie. Congestive heart failure is a condition we see mostly in smaller dogs, and occasionally in cats, that causes fluid buildup in the lungs secondary to what's going on with the heart. Think of the heart as a two-sided pump — when the top chambers squeeze, they push blood through what's supposed to be a one-way door, and when the bottom chamber squeezes, it slams that door shut. Those valves make it one-way, so blood pumped out doesn't flow backward. But in dogs with congestive heart failure, and cats with congestion, we see valvular dysfunction. A lot of these dogs have murmurs, sometimes for years, before they become actual heart failure patients — because a murmur is not disease. A murmur is the sound blood makes when, instead of a true closure, the valve overcloses or the leaflets aren't shaped right, and blood goes backward. A lot of dogs aren't symptomatic from that; they're not in congestive failure. But at some point, when that process gets advanced enough, you've got the right side of the heart pumping blood into the lungs because that's its job, and the left side also pumping blood into the lungs because it's going the wrong direction. That's a lot of blood under pressure in the lungs, and blood under pressure in a vessel starts to leak fluid. When that fluid leaks into lung tissue, it affects how well the dog can trade oxygen for carbon dioxide, and frequently these dogs start coughing.
Dr. LoSassoClassically it's our smaller dogs — typically 20 pounds or less, though that's not a hard rule. Chihuahuas, Schnauzers, Dachshunds — but the poster child for congestive heart failure is the Cavalier King Charles. They're very well known for left-sided heart disease, which is a tragedy because they're the sweetest creatures on the planet. Those dogs start to cough a little, and sometimes vets will treat them with antitussives, cough suppressants — that doesn't help if the problem isn't irritation, if it's actually fluid in the lungs. So how do you diagnose it? You can definitely look with X-ray. I actually find fairly frequently that I just use ultrasound. I was taught back in the day that you can't look at lungs with ultrasound because they're full of air and all you get is artifact — and that's absolutely true if the lungs are dry. But if the lungs are full of fluid, I can see that very distinctly and grade the lungs with ultrasound. It's often a little cheaper, and it's definitely less stressful — they don't have to lie on their backs like they do for X-ray. Sometimes, if the dog is cooperative enough, I can just stick my hand through the door of our oxygen cage without anybody holding them and check how wet the lungs are.
Dr. LoSassoAcute treatment, when they come in to us, is an oxygen cage — we effectively double the oxygen they're breathing. You and I right now are breathing about 20% oxygen; we can get our oxygen cage up to about 40. That makes it a little easier for them, but if they have a physical problem trading oxygen for carbon dioxide, it doesn't come anywhere close to solving the problem. What we have to do is dry those lungs out — we give them a kidney drug called Lasix, or furosemide, which pulls water from the body. The first place we notice that happening is the lungs; as they dry out, breathing gets much easier and respiratory rate drops. If we can successfully treat them with furosemide and keep them in oxygen, we can eventually wean them off oxygen, and they go home typically on oral furosemide plus a couple of heart medications. If I had an older dog with a murmur, I'd talk to my veterinarian about starting one of those heart medications prophylactically — dogs with murmurs put on pimobendan, studies have shown, may have the onset of congestion delayed, or in some cases prevented entirely. The real struggle is with the Cavaliers, because we all know they're going into heart failure at seven or eight years of age. Occasionally we'll see some live longer, but it's pretty frequent that we see what we'd normally consider middle-aged dogs with a very old dog problem — they've got old dog hearts even when they're young.
JulieWhat can pet parents understand — if they're starting to see symptoms they suspect could be congestive heart failure, what should they do, and how advanced could it be by the time symptoms start showing?
Dr. LoSassoIt's pretty well down the line by the time they have enough breathing trouble that people bring them to me — usually it's "yeah, he's been coughing for a couple months." I'd be very concerned about a persistent cough in a small breed dog, especially one that's 12, 13, 14 years old, because that could very well be heart disease, and I'd get it checked out with X-rays or ultrasound. I don't know that a lot of general practices in our area use ultrasound, but they certainly could to look at those lungs and determine if they're wet. You can't just go by the murmur — the murmur doesn't tell you if there's congestion. It just says there's inappropriate blood flow. Dogs in congestive heart failure almost always have a very significant murmur, but you can have a very significant murmur and not have heart disease. You have to look farther, either with X-rays or ultrasound.
JulieCan you touch on cats? You mentioned before we started recording that treating cats is quite challenging.
Dr. LoSassoTreating cats is really difficult. Occasionally we'll see a cat come in with congestive heart failure — they generally have something called hypertrophic cardiomyopathy, but the label isn't that important. They're in congestion, and we treat them with Lasix and oxygen just like dogs. Once we can get them out of oxygen, they generally need a combination of pimobendan, and we put them on Plavix too, because those cats are very prone to clot formation — it's a drug that prevents platelets from aggregating and forming clots. The real challenge with cats is that most people either don't want to, or aren't able to, give oral medication twice a day. It's a genuine struggle for cat owners, and a lot of cats end up not being treated nearly as long as dogs, strictly because of the difficulty of giving oral meds — if you get the pill bottle out and your cat's hiding under the bed, it's a real struggle, and it changes the relationship. It's genuinely challenging in cats.
JulieAre cats' symptoms similar to dogs?
Dr. LoSassoNot really. They generally don't cough like dogs do. You don't know they're really in trouble until they're not moving around much — they're open-mouth breathing, their respiratory rate is really high. It catches a lot of people off guard, and heart disease in cats in general is a silent killer. We see cats born with that same hypertrophic cardiomyopathy who are simply found dead, or have a clot event, at two or three years old — something they were born with, no murmur, no indication of any problem whatsoever until you find them struggling with a clot or passed away. It's very sudden, and it's tough.
JulieHow often do you see this? Is it one of the more common conditions?
Dr. LoSassoI haven't actually seen it in a few weeks, so I'd say on average we see maybe one congestive heart failure dog every couple of weeks — but I've also had all four of my oxygen cages full of congestive heart failure dogs at the same time, so it really depends. I'd say 40 to 50 times a year, maybe.

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