Hi. My Dog Is 10 (american Bulldog) And Has Been

Hi. My dog is 10 (american bulldog) and has been coughing frequently. I had xrays taken about 6 mths ago and they couldn't find anything wrong except his heart looked enlarged. Over the past couple of days, he's been very lathargic and his hind legs seem to be bothering him. He had both knees operated on years ago, but this seems related to the heavy breathing and coughing.