My basset Rosco is about 7 yrs old. He has a very sensitive stomach. He was rescued from a very abusive situation and he spent a lot of time on the street. After a 4yr treatment, he is finally heartworm free. I have heard that some anti-flea and tick treatments can also prevent heartworm but I am afraid they could upset his stomach. It took me years to bring him back to health and he is such a wondeful dog I want to make the rest of his life pleasant. Any thoughts?
Thanks for your help.

Thanks for your help.