Merck Manual

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Stages of Heartworm Infection in Dogs

Stages of Heartworm Infection in Dogs

Stage

Signs

I

Minimal, if any, signs and none evident to owner

II

Mild to moderate signs of HWD, most often including cough

III

Severe signs of HWD, including respiratory signs, weight loss, exercise intolerance, and even heart failure

IV

Caval syndrome