We've spent 200 bucks on our dog in medical since we got him back in the mid 90s.
He had kennel cough last year which is a respiratory infection that he caught from another dog that we gave him some medicine for. Never been on heartworm prevention or anything. Had him checked for that when he had kennel cough and after 12 years heart worm free.

He is also an inside dog so the risk of him getting heartworms is greatly reduced...