Your vet can test for heartworms with a simple antigen test — a quick blood test that detects proteins released by adult female heartworms. Results come back in about 10 minutes, and it's typically included in an annual wellness visit.

A few important things to know about testing:

• Annual testing is recommended even for dogs on prevention. No preventive is 100% effective, and catching an infection early makes an enormous difference in outcome.

• A negative test doesn't always mean the all-clear in a newly infected dog. Antigen tests don't turn positive until adult female worms are present — which takes about 6–7 months from initial infection. If your vet suspects recent exposure, they may recommend retesting.

• Your vet may also check for microfilariae (baby heartworms in the bloodstream) using a separate test — combining both tests gives the most complete picture.

If your dog tests positive, your vet will likely recommend chest X-rays, bloodwork, and sometimes a heart ultrasound before starting treatment, to understand how severe the infection is and how to treat it safely.