How Long Can a Dog Live with Heartworms Untreated? (& Survival Rate)

sad dog on couch with heartworms

If you’re a dog parent, you know how dangerous heartworm disease can be for your beloved pet. The condition starts off slow and subtle but eventually turns into something lethal.

Luckily, the effects of heartworm disease take some time to reach the point of no return. So, as long as you get the proper treatment on time, your dog could be healthy again. But how long can a dog survive with heartworm infection untreated?

This question has answers that are dependent on many factors and it’s difficult to know exactly how long your heartworm-infected dog can survive without treatment, but we explore that question in detail and provide answers.


  • Dogs can survive for at least 6-7 months from the date of infection, as that’s how long an adult heartworm takes to mature. But it’s difficult to pinpoint the date of infection.
  • If treated in stage 1 or 2 of the infection, your dog can usually live a normal, healthy life afterwards
  • If treated in stage 3 or 4, the likelihood of organ damage is high, leading to heart failure and/or lung and respiratory disease. This would reduce the life-expectancy of your dog

Let’s look at this question in greater depth…

Can a Dog Survive Heartworm Disease With No Treatment?

The short answer? It’s possible a dog can survive if a dog doesn’t reach a stage 4 heartworm infection. These are the most severe cases. (we discuss different stages further in this article)

However, heartworm disease is a serious condition that still requires appropriate treatment to stop your dog’s suffering, no matter which stage of infection your dog is at.

Your dog will not survive if left in this condition, especially for a prolonged period and it will unfortunately suffer for that period.

Heartworm disease in dogs has four stages of infection, causing them to undergo symptoms ranging from mild, uncomfortable, to absolutely fatal.

You can see the life-cycle of heartworms in their different stages in this video below:

The final stage of heartworm infection is called Caval syndrome, a condition where massive hordes of worms start blocking the blood flow to the heart.

If your dog has reached this stage, the chances of survival are quite low, and surgery is often the only method of treatment – and even this is not guaranteed to work and the risk of death is high.

You can only save dogs with Caval syndrome after surgically removing the adult heartworms blocking the blood flow.

However, it is common for infected dogs to sadly die even after undergoing surgery or during the procedure.

How Long Can Dogs Live with Heartworm Disease Without Treatment?

How long a dog can survive without treatment depends on how serious the condition is, but the short answer is, at least 6-7 months from the date of infection. But the answer is more complex..

Heartworms occur when a dog gets bitten by an infected mosquito with microscopic heartworm larvae, which pass into the dog’s blood through the bite wound.

Once this happens, it can take around 6 to 7 months for the larvae to grow and become adult heartworms.

Once matured, the adult heartworms breed with each other, prompting the female heartworms to release more juvenile heartworms into your dog’s bloodstream.

Naturally, this causes the disease to spread rapidly, provoking more symptoms to surface.

As mentioned earlier, the disease has four stages with varying symptoms and levels of severity.

Since most of the symptoms are only detectable after the heartworms have matured, we can assume that most dogs can live for at least 6-7 months after infection.

However, the chances of survival decrease rapidly once the adult heartworms have completed their life cycle and reproduced, pushing the infected dog further towards Caval syndrome.

So, to conclude, your dog will survive the first 6-7 months of infection but will worsen after this period.

After the initial period, it’s only a matter of several weeks to a month until the disease reaches the final stage, after which your dog will quickly deteriorate and sadly pass away.

You must treat heartworm disease as soon as possible for the best outcome.

Survival Rate for Heartworms in Dogs

Most dogs can overcome heartworms and live a healthy life if given the correct treatment and care.

However, without any treatment, the rate of survival for heartworm-infected dogs is extremely low, especially if it has progressed to the final stage.

It’s difficult to give an exact figure as different dogs have different worm burdens or are at different stages.

However, we can say that once the disease has developed into Caval syndrome, it is extremely likely that the dog will die without surgical intervention.

Heartworm Prevention: How to Stop My Dog Getting Heartworm Infections Again After Treatment

Heartworm disease can come back to infect your dog again even after effective treatment, so a heartworm preventative schedule is a must.

It is always a good idea to take preventive measures to ensure this doesn’t happen again.

The last thing you want to see after this traumatic experience is your dog tests positive again.

In fact, once a dog gets infected with heartworms, doctors suggest owners continue with heartworm prevention methods for the rest of their life.

Simply put, the treatment for heartworms never ends.

What Preventative Heartworm Medication Will Be Prescribed?

Your vet will prescribe an FDA approved heartworm preventative medication for your dog.

It will depend on your vet and their recommendation but products can include

  • topical liquid applied on dog’s skin
  • oral tablets once a month. 
  • injections every 6 months to a year

The good news is that some of these products also prevent against other parasites like:

  • hookworms
  • roundworms
  • fleas
  • ear mites
  • ticks

It’s also important to know, does dog heartworm medicine expire? < Be sure to check out our comprehensive guide to this important question because the answer depends on a few things.

Vets will typically conduct a heartworm test to accurately detect infections 6 months after your dog has been treated.

This is to ensure that all heartworms have been eradicated from your dog’s system.

The best way to confirm whether or not there are any heartworms left is to run a heartworm antigen test.

Most dogs will display signs of complete recovery at around 16 weeks post-treatment, with antigen tests coming up as negative.

However, this doesn’t mean that you’re in the clear.

Doctors recommend running tests every other month to determine the extent of recovery and detect signs of re-infection.

There are a few questions relating to treatment we constantly see and decided to write a comprehensive guide on each.

Like, can you deworm a nursing dog?

Or whether you can use horse wormer on dogs and if so, how much safeguard horse wormer to give a dog.

Heartworm Disease Survival: FAQ’s

Given below are the most frequently asked questions regarding how long a dog can survive heartworm disease without treatment.

Can a Dog Live a Long Life After Heartworm Treatment?

Yes, a dog can live a long life after heartworm treatment with the proper care, but it also depends on the stage you catch this potentially fatal disease.

If treated in stage 1 or 2 of the disease, it’s likely there will be no lasting damage to their organs or long-term health issues. (we discuss the different stages under the next heading)

If treatment was administered at stage 3 or 4 of infection, then it’s far more likely that there has been damage to a dog’s organs like the heart and lungs most commonly, but also potentially the kidneys and liver.

If this is the case, your dog will need to be on treatment for heart failure for life and life-expectancy is reduced.

It also depends on how you manage the care of your dog after the active heartworm infection is over.

When adult heartworms die after a severe heartworm disease, they can still pose a threat if your dog is overly active as this can lead to them blocking blood vessels.

Your dog’s body takes time to break down the dead worms and remove them from the bloodstream.

Heartworm disease in dogs is only fatal once it reaches the final stages of infection, which mostly happens when the disease is left untreated for up to 7 months, giving rise to more and more adult heartworms.

You can effectively kill all heartworms by having your vet administer heartworm medication like melarsomine injections.

A 3-dose protocol by the AHS is the most effective solution to treat this serious condition as efficiently as possible.

Once the infection has been treated, your dog may live a long and healthy life if the damage caused hasn’t been severe, however a heartworm preventive is always better than a cure.

This is because treatment for heartworm disease in dogs is harsh and can come with side effects of their own.

When the treatment is over, you should keep going for heartworm tests throughout your dog’s lifespan and always use heartworm preventives so they can eliminate infective worm larvae from infected mosquito bites instantly.

What Happens to A Dog with Untreated Heartworm?

There are 4 stages of heartworm disease ranging from mild (Stage 1) all the way to severe (Stage 4).

Dogs with heartworm disease show symptoms like:

  • Mild persistent cough
  • Excessive lethargy and fatigue after activity
  • Weight loss
  • Muscle loss
  • General tiredness and exercise intolerance
  • Appetite loss

You can read our guide on what to feed a dog with heartworms if you’re finding their appetite has reduced.

Stage 1

Usually starts with a mild cough. Sometimes there won’t be any symptoms of heartworm at all at this stage

Stage 2

At this stage your dog will usually start having a more persistent cough and you’ll notice more lethargy and tiredness, especially after bouts of activity.

Stage 3

Symptoms become more obvious visually, with a loss of weight, breathing problems, persistent cough. Your dog will look visibly sicker. This stage is likely where heart failure and severe lung disease begins.

Stage 4

The worm burden inside your dog at this point will lead to potentially serious complications. A great number of worms will now be blocking blood going to and from the heart and the only solution at this stage is risky surgery to remove the blockage. Unfortunately, many dogs will still die during or after surgery.

A dog infected with heartworm may never progress to stage 4 if their worm burden consists of only a few worms.

Dog owners should immediately start treatment at the earliest clinical signs of heartworm.

Canine heartworm disease can become fatal if left untreated for up to 7 months.

This is when the heartworm larvae mature into adults and reproduce, with the adult female heartworms releasing more offspring into your dog’s bloodstream.

Once the infection reaches this stage of severity, it becomes very unlikely for your dog to survive, even after the final resort of surgery to remove the worms.

This is because the worm load is too great and severe damage to your dog’s heart may have already been done.

Summary and Final Word

Although we can’t put an exact timeframe on it, we do know that heartworm disease eventually can become fatal if left untreated.

If you have a heartworm-positive dog, we recommend taking him to the veterinarian right away to undergo treatment.

Even if you aren’t sure, go and get your dog tested with blood tests that can accurately detect heartworm proteins, infections from infective larvae and immature heartworms to adult worms (there are different tests for each).

Heartworm disease shows symptoms from the first stage, but they are mostly undetectable.

We recommend administering regular heartworm testing for dogs that are several months old to accurately detect heartworm infections.

Your vet can treat heartworm by injecting your dog with melarsomine shots, a medical drug that can effectively kill adult heartworms infesting your dog’s body.

Remember to go for regular tests even after treatment has been completed to know if the heartworm treatment was effective, and starting heartworm prevention is a must.