Heartworm disease causes severe suffering in dogs through progressive cardiac and pulmonary damage, but is almost entirely preventable through inexpensive monthly medication.
Heartworm disease causes a slow, progressive deterioration in dog health and quality of life. Dogs with heavy worm burdens experience chronic coughing, reduced exercise tolerance, and eventually congestive heart failure — a condition involving fluid accumulation, breathing difficulty, and profound weakness. Treatment is itself a welfare challenge: dogs must be strictly confined for months while dead worms are reabsorbed, and the treatment carries risks of fatal pulmonary embolism. The contrast between this suffering and the simplicity of prevention makes untreated heartworm one of the most avoidable welfare harms in companion animal medicine.