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Heartgard 51-100 pounds
http://www.amazon.com/gp/product/B00ULLVIXQ/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=B00ULLVIXQ&linkCode=as2&tag=cockers-20&linkId=QHKKHNGFWOGEQPXN
Think BROWN for BIGGEST, This will be for very heavy-set American cockers, or most English cockers. And don’t forget to use the cute little stickers in each pack to put on your calendar to show you have done it. I stick them on and then put a big checkmark each month to show me that I have done it.