I have a 10 year old chocolate lab that tested positive for heartworms about a year ago. At that time my 8 year old lab also tested positive an recieved the 'arsenic' treatment. It was hard on him, so we decided to hold off through the HOT summer to treat TUG ( 10 yr old), due to his old age. The heartworms didn't seem to have effects throughout the winter, however, yesterday he began coughing/choking all day and all night. Is it to late to treat him? What can I do to relieve his symptoms? Is there another option for treatment? Is there a treatment suited for older dogs? thank you for your time, I feel ours is of the essence. Kasey Kimmons