Mosquitoes may not be around in the winter, but he could have contrated Heartworm a long time ago. It takes quite awhile for the heartworms to become large enough and in enough quanity before they start to cause problems. :(
I would be looking for a second opinion.
I hope Sebastion is feeling better soon.
I would be looking for a second opinion.
I hope Sebastion is feeling better soon.
