I am not a vet but have dealt with heartworm treatment several times. I have had hunting dogs near 50 years. One dog had the old arsenic treatment which required total rest and limited movement. Infestation was several years along and dog never really was the same.
My last experience was with a 5 year old German Shorthair I acquired in 2015. He was never on preventive and had heartworms. I basically did what I had done at least 2 other times. I started him on monthly Ivermectin and let nature take it's course.
I know Vets are against this, but it basically kills the larvae and prevents other worms from developing. Adult worms are said to live somewhere between 2 to 5 years last I read. So over time the dog can be heartworm free. Max died at the age of 11 in 2021 from cancer and hunted and ran well up till near the end.
I believe it depends how long and how severe the infestation is that dictates success. If the damage is done. No treatment is gonna reverse that. Your dog seems young and hasn't probably had adult worms long. You may have options. My statements are just my personal experiences.
In the end, learn all you can about the treatments, listen to a vet you trust and do the best you can. Good luck.
