Should I buy/use Doxycycline on my dog with heart worms??!?

what a vet will normally do simply put will rip you off and they will offer you everything and anything and due to that fact they try to mock each other and put each other down so what you want to do is ring another vets in the area and explain what the last vets have done and what they have gave you just ask for a second opinion for your dog, and then they will most probably say "oh i dont know why they have gave you them you dont need them you need these" then offer you something different. then you ring another vets and see what they offer you and by the end of the day you will have a big long list, and you go with what the majority are saying you need, but if you have already paid for the medication , ring the vets you got them from and explain you have been on the internet and seen some people saying they didnt work for your dog and tell them you want reaasurance and maybe they will say well if this happens then will sort it out free, put the responsibility on their toes