Heartgard for dogs can be used with or without a meal. However, it is recommended to give Heartgard to small dogs with a meal. This is because feeding your dog before or during administering the medication can help reduce the risk of stomach upset or vomiting. Additionally, giving Heartgard chewable with a meal may help improve the absorption of the medication. When taken with food, the medication is more likely to be absorbed and metabolized properly, increasing its effectiveness in preventing heartworm disease.