What You Need To Know About Heartworm Disease

Chili Pepper came to Singapore with her family in 2012. During a health check with Dr Sarah Wong, Mount Pleasant (East), we discovered through a blood test that she was infected with heartworms. With strict exercise restriction and treatment, Chili Pepper recovered. She is 10 this year.


“Chili Pepper is a present for our wedding in 2006. I went to London to pick her up when she was 3 months young & we lived in Roma, Italy till 2012. She is adorable. Loves toys & food.” ~ Tatiana


“I like the name Chili. My husband likes Pepper. So here we have Chili Pepper. Chili Pepper loves water and can swim all day long – she’s a dog fish!”

What is heartworm disease?

Heartworm disease is a serious, progressive and potentially fatal disease. It is caused by a parasite Dirofilaria immitis which is transmitted by mosquitoes. Heartworm disease occurs mostly in dogs and less commonly in cats. Early detection is essential for successful treatment.

How is Heartworm disease transmitted?

Ref: dogaware.com

When a mosquito bites an infected animal, it picks up microscopic baby worms called microfilariae in the blood, which then develop into “infective stage” larvae. When this infected mosquito bites a dog, the larvae are deposited under the dog’s skin. It takes about 6 months for the larvae to mature into adult heartworms which lodge in the heart, lungs and surrounding blood vessels where they reproduce.

which DOGS are MORE at risk?

All dogs who are not on heartworm prevention are at risk of heartworm infection. Dogs living in landed properties and those who regularly walk in mosquito-prone areas are at higher risk.

How does heartworm disease affect my dog’s health?

Heartworms live in the heart, lungs and associated blood vessels where they mature and reproduce. In the early stage, your dog may not show any symptoms. As the number of worms increases, signs of heart failure develop. E.g. weakness, exercise intolerance, coughing, decreased appetite, weight loss. 


An adult heartworm can grow up to 30cm long.

what happens when heartworm disease is not treated?
  • Some dogs may harbour several hundred worms which cause lasting damage to the heart, lungs and arteries.
  • In severe cases, the abdomen and legs will swell from fluid accumulation.
  • The disease can lead to liver or kidney failure causing jaundice, anaemia and accumulation of toxins.
  • Severely affected dogs can develop a sudden blockage of blood flow within the heart leading to a life-threatening form of cardiovascular collapse called caval syndrome.

Ascites (fluid accumulation in abdominal cavity) giving your dog a pot-bellied appearance.

How is heartworm disease treated?

Most dogs with heartworm disease can be successfully treated, especially in the early stages. The goal is to kill the microfilariae as well as adult worms through a series of injections while minimising the side effects of treatment. Dogs with advanced heartworm disease may require antibiotics, pain relief medications, diuretics to remove fluid accumulation and drugs to improve heart function.

The adulticide drug is given by deep intramuscular injection into the lumbar (lower back) muscles of the dog. Junior is an ex-breeding farm dog we are helping under Mount Pleasant Gives Back. With good care by her adopter Liz and family, her health has improved and she is ready for heartworm treatment at Mount Pleasant (Bedok). Her new name is Maz.


“It was a nightmare when we discovered Chili Pepper had heartworms. Dr Sarah Wong helped me understand the disease & gave me the support needed. An amazing person & vet. Chili Pepper went through treatment & we restricted her activity strictly. She put up a good fight & won!”

complete rest is essential during treatment

During treatment, it is very important to restrict exercise to decrease the chance of complications, especially pulmonary thromboembolism (clots in the vessels) as the worms die off. Signs of embolism include coughing, low grade fever and sudden breathing difficulty. 

  • No running, playing, jumping.  
  • Slow and short walks on leash.
  • Active, playful dogs need to be strictly confined to rest.
  • Some dogs need to be hospitalised for a few days.

A heartworm test will be done 6 months after treatment to confirm that all heartworms have been eliminated. Some dogs may require lifetime medication for heart failure.


“Chili Pepper is 10 years old now. We love her like one of our kids. We understand that even when all the worms are eliminated, the heart may already be damaged. Since the treatment, Dr Sarah has been monitoring Chili Pepper’s heart. “

How can we prevent heartworm disease in our dogs?

Preventive Medication: Consult your vet on the appropriate heartworm preventives for your dog, e.g. pill, spot-on topical medication or injection to eliminate immature heartworm parasites.

Blood Tests: All dogs should be tested annually for heartworm infection as part of preventive care. If your dogs are older than 6 months and not on heartworm preventive, a simple blood test is done to ensure they are not already infected by the parasite before starting preventive medication.

Because no preventive medicine is 100% effective, annual testing is necessary to ensure the preventive medicine is working and to detect any infection in the early stage. 

Mosquito Control: Remove any containers that may collect water. Clean out rain gutters regularly. Keep the grass short and rake up fallen leaves (which can hold water) to reduce breeding sites.


“Chili Pepper is currently on heartworm preventives & heart medications. She is responding well. Happy & playful at home. We hope it will be like this for a long long time.”