No, I've never had this problem with my dogs. Does your pup upchuck his/her meal more than occasionally, have a sensitive stomach? Is it the Heartguard chewable formula or the pill? I'd definitely let the vet know. If he/she threw up shortly after having received the dosage, you have to assume he/she has not been covered for that month. Missing two dosages puts your pup at high risk of infection. Definitely let your vet know