I started researching about Ethoxyquin when I found out that Solid Gold's products use it. What I don't like is that Solid Gold gets their fish from a different company, so they do not have to list the use of Ethoxyquin in the ingrediants on their packaging. Ethoxyquin is used to preserve their fish in the "Wee Bits" formula. I emailed them awhile ago to ask about it and didn't receive a response. Ethoxyquin has been banned from most human food because it causes cancer (amongst other things). Scarey stuff!
This is why I homecook, then I know exactly what is in their food. Anyways, on to your question. Isn't Ethoxyquin used to preserve fats? Would their be any fats in Heartguard? I don't think so. Hmmm