Veterinarians classify heartworm disease in four stages:
Class 1, Mild
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No symptoms or an occasional cough.
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Often only caught through annual testing.
Class 2, Moderate
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Occasional cough, tiredness after exercise.
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Dog may seem "off" but functions normally.
Class 3, Severe
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Persistent cough, significant exercise intolerance, labored breathing, weight loss.
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Signs of heart failure may be present.
Class 4, Caval Syndrome
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Life-threatening worm blockage.
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Requires emergency surgical intervention.
The earlier heartworm disease is caught, the better the outcome. A dog in Class 1 treated promptly has an excellent prognosis. Class 4 is a fight for their life.