What causes heart failure in dogs?

That moment when your dog slows down mid-play, tongue lolling more from exhaustion than excitement, can send a little pang of worry through any owner. A tired pup is normal after a long walk, but when that fatigue sticks around—when they struggle to catch their breath after climbing stairs or cough softly at night—it might be a sign something’s up with their heart. Heart failure in dogs isn’t a single problem, but a result of things that weaken that hardworking muscle over time, and understanding those causes can help you spot trouble early.​

Some dogs are born with a higher risk, thanks to their genes. Breeds like Cavalier King Charles Spaniels often deal with weak heart valves from a young age—valves that don’t close tight, letting blood leak backward and making the heart work overtime. Great Danes and Dobermans, on the other hand, sometimes inherit a condition where the heart muscle itself grows too thick or becomes too thin, struggling to pump blood efficiently. These aren’t anyone’s fault; they’re just part of the breed’s makeup, which is why responsible breeders screen for these issues before pairing dogs.​

Age creeps in, just like it does with us. As dogs get older, their heart valves can stiffen or wear down, a lot like how a door hinge gets creaky over time. This slow breakdown means the heart has to pump harder to push blood through, and over years, that extra work takes its toll. You might not notice it at first—maybe they nap a little more, or don’t race to the door when you come home as quickly. Those small changes are easy to brush off as “just old age,” but they’re worth mentioning to your vet.​

Other health issues can sneakily damage the heart, too. High blood pressure, often linked to kidney disease or thyroid problems, forces the heart to work harder to push blood through narrow vessels. Infections like parvovirus or even a bad case of heartworms—those tiny parasites that hitch a ride through mosquito bites—can inflame the heart muscle, leaving scar tissue that weakens its function. That’s why staying on top of preventatives, like heartworm medication (required in many areas), isn’t just a good idea—it’s a way to protect their heart.​

What they eat and how active they are matters more than you might think. Obesity piles extra strain on the heart, making it work harder to supply blood to all that extra tissue. A diet high in sodium can also raise blood pressure, adding to the problem. On the flip side, too little exercise weakens the heart muscle over time, just like it does in humans. It’s a balancing act: keeping them at a healthy weight with regular walks and a nutritious diet goes a long way in protecting that vital organ.​

Sometimes, the cause is a mystery—no clear breed link, no other health issues, just a heart that starts to struggle. That’s why regular checkups are so important. Your vet can listen for a heart murmur (that swishing sound instead of a clear “lub-dub”) or notice changes in their breathing rate that signal trouble. Catching these signs early means more options to manage the condition, keeping them comfortable and happy for longer.​

Watching your dog’s heart struggle is scary, but knowing the causes helps you be proactive. It’s about those regular vet visits, keeping up with preventatives, and noticing when “normal” changes. Their heart works tirelessly for them—giving it a little extra care in return is the best way to keep those tail wags going strong.