Petco Text Logo
Petco Pet Logo

When should my new puppy start heartworm medicine? Is testing needed?

Updated On September 23rd, 2025

Pet's info: Dog | Mixed Breed Small (up to 22lb) | Male | unneutered | 2 months and 3 days old | 3.5 lbs

We just got a 9 week old, 3.5 lb. Puppy. When should he start heartworm medicine, which one is the safest, and does he need tested first?

1 Answer

Most Helpful Answer

Image profile

Answered By Jennifer Summerfield, DVM CPDT-KA

Veterinarian, Certified Dog Trainer

Published on June 22nd, 2019

Hi there. Your pup is old enough to start on heartworm prevention now. I would suggest using Heartgard or Sentinel - both of these are fine for a pup who is 9 weeks old and weighs 3.5 pounds, and both are very safe in general. Puppies under six months of age do not need to be tested first.

Vote icon

5Pet Parents found this answer helpful

image
Have A Vet Question?

Book an appointment with the pros – our expert vets are here to help.

Sponsored