How do i know if my dog has heartworms?

A dog needs to see a vet asap to have blood work done in order to be tested for heartworms. Also, it's important to your dog is tested negative fir heartworm before starting any prevention pill.

Symptoms of a heartworm infection can take months to appear. Here are some of the common signs that a dog has heartworms.
A soft, dry cough The parasites make their way to the lungs and start multiplying in the lungs and surrounding veins. Coughing may be most noticeable after exercise and may end with fainting. Inactivity or lethargy Your pet suddenly seems tired more often, doesn’t want to go outside, or avoids all physical activity Weight loss or anorexia Rapid or difficult breathing Bulging chest Allergic reaction Collapse Other symptoms are possible, too: Nosebleeds Secondary pneumonia Increased blood pressure Excessive sleeping Seizures Blindness Lameness You should take your dog to the Vet if any of these symptoms exist. Blood tests to detect the various stages of infection can include viewing a blood sample under a microscope and checking for antigens of adult heartworms (a protein the heartworms produce and also the most commonly used test)