Can you tell if a dog has heartworms by their poop?

Can you tell if a dog has heartworms by their poop? It’s a question that might pop into your head while scooping up after your pup during a morning walk—especially if you’re new to dog ownership. Let’s say you notice their stool looks a little off, maybe softer than usual, and suddenly you’re spiraling: Could this be a sign of something serious like heartworms? Spoiler: Probably not. But understanding why, and what to look for, can help you keep your furry friend healthy.

First, let’s get clear on what heartworms are. These tiny, thread-like parasites are spread by mosquitoes, not through feces. When an infected mosquito bites your dog, it deposits heartworm larvae under their skin. Over months, those larvae migrate through the body, eventually settling in the heart and nearby blood vessels, where they grow into adults. Here’s the key point: Adult heartworms live in the circulatory system, not the digestive tract. They reproduce, but their offspring (microfilariae) float in the blood, not the stool. So unlike intestinal parasites like roundworms or hookworms—whose eggs or larvae do show up in poop—heartworms leave no trace in your dog’s waste. Last year, my friend Jake learned this the hard way. His Lab, Max, had been lethargic, but Jake brushed it off because Max’s poop looked normal. It wasn’t until Max started coughing during their evening hikes that the vet ran a blood test and found heartworms. “I wasted weeks checking his stool,” Jake said. “Turns out, that’s not how it works.”

So if poop isn’t the clue, what is? Heartworm symptoms show up when the parasites grow and block blood flow. Watch for a persistent cough, especially after play or exercise—think of it as your dog struggling to catch their breath. You might also notice they tire easily on walks they used to breeze through, or they lose weight even though they’re eating normally. In severe cases, their belly might swell from fluid buildup. These signs usually take 6-7 months to appear, which is why early detection matters. The only reliable way to check for heartworms is a blood test, which your vet can do during annual exams. In areas with lots of mosquitoes—like the Southeast or along the Gulf Coast—vets often recommend testing twice a year, just to be safe.

Preventing heartworms is way easier than treating them, and it’s something every new owner should prioritize. Most vets prescribe monthly chewables or topical treatments that kill larvae before they mature. They’re easy to incorporate into your routine—set a reminder on your phone, and give it to your pup with a treat. My neighbor Sarah hides hers in a piece of cheese; her Beagle, Lucy, thinks it’s a snack, not medicine. If you miss a dose, don’t panic, but call your vet—they might suggest a booster or an extra test. Remember, prevention is affordable compared to treatment, which can cost hundreds of dollars and involve months of medication or even surgery.

As a dog owner, there are other habits to keep in mind, too. While heartworms aren’t spread through poop, cleaning up after your dog is still a must—many communities fine owners who leave waste behind, and it’s just common courtesy. When walking, keep your dog on a leash in public spaces, not just to follow local laws but to avoid skirmishes with other animals that might carry pests. And never scold your dog for symptoms like coughing—they’re not being “naughty”; they’re in discomfort. Instead, reward them with praise when they let you check their gums (pale gums can be a sign of trouble) or when they take their preventive medicine. In apartments, keep windows screened to keep mosquitoes out, especially at dawn and dusk when they’re most active. And don’t skip those annual vet visits—they’re not just for shots; they’re your chance to catch issues before they get serious.

At the end of the day, your dog’s poop tells you a lot about their health—but heartworms aren’t on that list. Stay vigilant for the real warning signs, stick to prevention, and keep up with vet checkups. That’s the best way to make sure your pup stays happy, healthy, and ready for all those walks, fetch sessions, and cozy evenings on the couch.