I use Greenies pill pockets. They are little cylinder-shaped treats with the consistency of playdough. They have an indentation in the middle so you can put the pill in and then pinch it shut. Every month, Thor will do around six tricks in a row for these, he loves them so much. Since they are so soft, he doesn't chew them, so I never have any problems with him discovering heartworm meds inside.
I've never had to give him liquid medicine.
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I see I posted at the same time as
PenniesMom. Yeah, pill pockets rock.