I have an 8yo Cavalier King Charles who is on Vetmedin and has been for over a year, he has a very enlarged heart (you can feel it beating terribly) and started fainting, he is quite happily walking along, you see a little wobble and then he falls down, stays there panting and scrabbling for a little while (it is horrible to see) and then gets up, he was having about 10 faints a day, but with vetmedin (which he loves, waits every morning and night by the place it is kept for his tablet) it is about 1 or 2. He is very underweight, but still basically happy if a little tired. Unfortunately now he needs diuretics as his heart condition worsens, but I would happily put a dog on vetmedin from my experience, it has certainly made a difference to my boy. Having 10 faints meant we really couldnt take him anywere off lead, and that is what he loves. He can't keep up with his friends (two 12 year olds!!!) but he potters round the horse fields and gets up the hill in his own time. I do hope it helps your dog.