Symptoms of heartworm in pets include coughing and unusual intolerance to exercise. In severe cases, a pet may show symptoms of anemia and fainting spells, notes PetMD.
It may take more than 6 months for the symptoms of heartworm to appear, according to Petful. Common symptoms may include weight loss or anorexia, rapid or difficult breathing, bulging chest, allergic reactions and even collapse. Several other symptoms may include secondary pneumonia, nosebleeds, excessive sleeping, seizures and increased blood pressure. Heartworms may affect both dogs and cats and the disease may be difficult to diagnose because the symptoms are also common for other afflictions.