How Long Does It Take for Heartworm Symptoms to Show?

Heartworm disease develops slowly, which can make it difficult for pet owners to recognize early on. Understanding the timeline can help you protect your pet before symptoms ever appear. If you live in Long Beach, CA, regular preventive care and annual screenings are the best ways to stay ahead of these serious parasites.

The Early Stages: No Visible Symptoms

After a mosquito carrying heartworm larvae bites a dog or cat, the larvae begin to mature inside the body. This process takes several months. During the first 6 months, most pets show no signs at all, even though the infection is already developing.

Because symptoms don’t appear right away, veterinarians consider heartworm a “silent” problem early on. This is why yearly testing with a heartworm test is so important, even for pets who seem completely healthy.

When Symptoms Begin to Show

For most dogs, early symptoms may appear 6–7 months after infection, once the worms have matured into adults and reached the heart and lungs. Cats may show signs earlier or later, and their symptoms tend to be more unpredictable.

Common signs can include:

•             Mild, persistent cough

•             Fatigue after light activity

•             Decreased appetite

•             Weight loss

These symptoms often start gradually, making them easy to miss. Our vets near you can help determine whether these changes are related to heartworm or another medical issue.

Advanced Symptoms Take Even Longer

If heartworms continue to multiply, more serious symptoms may appear, including breathing difficulties, fainting, or signs of heart failure. At this stage, the disease can be life-threatening. Because dogs and cats can look healthy for months before reaching this point, early detection is key.

Why Prevention and Testing Matter

Heartworm disease is much easier to prevent than treat. Monthly parasite prevention, paired with yearly testing at your trusted veterinarian or animal hospital, offers the strongest protection.

Call Our Vets Near You to Schedule a Heartworm Test Today

At Bixby Animal Clinic in Long Beach, CA, we’re committed to keeping your pets safe with reliable testing and prevention options. If you’re unsure about your pet’s heartworm status or need guidance on the right prevention plan, call our team at (562) 426-4066 to learn more.