Coughing, especially a persistent dry cough
Fatigue or low energy after mild activity
Reduced appetite
Weight loss
Trouble breathing or rapid breathing
Swollen belly from fluid buildup
Fainting or collapse
Weakness
Exercise intolerance
Pale gums
Signs of heart failure
Diagnosis confirmed by a veterinarian through heartworm testing
Positive antigen test or microfilaria test
Abnormal chest X-rays or ultrasound findings