A heartworm test is a diagnostic procedure used to detect the presence of heartworms in dogs and cats. Heartworms are parasites that live in the blood vessels of the lungs, heart, and other organs. They are transmitted through the bite of infected mosquitoes. The test is usually performed using a blood sample from the animal to detect the presence of antigens or microfilariae (young heartworms) in the bloodstream. A positive result indicates that the pet has been exposed to heartworms and may require treatment with medication to kill the parasites. Regular testing and preventive measures are essential to protect pets from this potentially fatal disease.