We used to get Heartgard from the vet years ago because that was what was available. When the vet switched medications, our dogs would not accept the new medication without being hidden in a treat. This went on for years because we did not know we could order the heart worm medication that our dogs preferred online.
Now our dogs line up when it's time for their medication. They love the beefy taste and the chewy texture. We will never buy heart worm meds from another source.
The prices are less than the vet and the package is delivered promptly.