I don't know what brand you're buying, but are you reading the label to make sure it's real venison, heart? These store bought products you buy have many added ingrediants and he may not like something that's in them. I find it hard to believe that any k9 would turn away from real venison liver or organs. You can buy all those items from the supermarket and dehydrate it yourself with the oven. It doesn't matter if it's not fully dehydrated, because either way it's good for him. It's very important in this day & age to read labels; they can say anything they want on the front of the package, but the label has to be the truth.