My chihuahua is about 15 months old. When I got him 4 months ago he was not well taken care of so I immediately took him to the vet. They told me that he does have Heart Worms. The treatment is so strenuous and I'm worried about him not making it through it. Can I continue to give him the heart worm prevention pills and hope that eventually it will kill of the heart worm? He's not that old so I am hoping the heart worm isn't as bad in him as it always sounds. How long does it take heart worms to develop? How long is the life-span of a dog with heart worms with or without treatment? Will treatment effect my dog differently because he is so little?