I found that on the Pet Meds site and the Merial site...
http://heartgard.us.merial.com/pdf/Dog_information.pdf
"The Chewable should be administered in a manner that
encourages the dog to chew, rather than to swallow without chewing. Chewables
may be broken into pieces and fed to dogs that normally swallow treats whole."
Dog Heartgard Chewables - 1800PetMeds
What is the most important information I should know about Heartgard Chewable: Heartgard Chewable is a prescription medication available for dogs as beef flavored chewable tablets. The usual dose of Heartgard Chewable for dogs up to 25 pounds is 68mcg (blue box), for dogs 26-50 pounds is 136mcg (green box) and for dogs 51-100 pounds is 272mcg (brown box). The chewable tablets must be chewed and should not be swallowed whole. For dogs that normally swallow whole, the chewable tablets can be broken into pieces.
How should this medication be given: Give Heartgard exactly as directed by the veterinarian. If you do not understand the directions ask the pharmacist or veterinarian to explain them to you. Heartgard chewable tablets must be chewed. They should not be swallowed whole. Use with caution in collies. Heartworm testing should be performed prior to the start of prevention therapy. If the animal is off Heartgard Chewables for 6 months or less, start the medication and test after 6 months since microfilaria, that take 6 months to mature, will result in a positive test result. Store Heartgard chewable at room temperature. Do not remove the chew from its wrapper until ready to give the medicine. Keep this medication away from children and pets.