Prevention is better than cure so the best time to prevent the disease is as soon as they start developing. It is better to be cautious before it actually occurs, so the best time to protect our dogs from heartworm disease is when they are puppies. The medication is recommended to be safe when puppies are of 6-8 weeks. There is lot of medication available for the prevention of heartworm disease, Trifexis https://www.petcarerx.com/trifexis/22843 is one of them that protect our dogs from these nasty parasites. The tablet is a beef flavored which prevents dogs from heartworm disease and kills fleas too.